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  <h2>Table of Contents</h2>

  <ul>
    <li>
      <a href="#general">1. General/Software Feature Questions</a>

      <ul>
        <li><a href="#1.1">1.1 Can I set up a POP or IMAP server on
        UNIX/Linux/OSF/etc.?</a></li>

        <li><a href="#1.2">1.2 I am currently using qpopper as my POP3 server
        on UNIX. Do I need to replace it with ipop3d in order to run
        imapd?</a></li>

        <li><a href="#1.3">1.3 Can I set up a POP or IMAP server on Windows
        XP, 2000, NT, Me, 98, or 95?</a></li>

        <li><a href="#1.4">1.4 Can I set up a POP or IMAP server on Windows
        3.1 or DOS?</a></li>

        <li><a href="#1.5">1.5 Can I set up a POP or IMAP server on
        Macintosh?</a></li>

        <li><a href="#1.6">1.6 Can I set up a POP or IMAP server on
        VAX/VMS?</a></li>

        <li><a href="#1.7">1.7 Can I set up a POP or IMAP server on
        TOPS-20?</a></li>

        <li><a href="#1.8">1.8 Are hierarchical mailboxes supported?</a></li>

        <li><a href="#1.9">1.9 Are "dual-use" mailboxes supported?</a></li>

        <li><a href="#1.10">1.10 Can I have a mailbox that has both messages
        and sub-mailboxes?</a></li>

        <li><a href="#1.11">1.11 What is the difference between "mailbox" and
        "folder"?</a></li>

        <li><a href="#1.12">1.12 What is the status of
        internationalization?</a></li>

        <li><a href="#1.13">1.13 Can I use SSL?</a></li>

        <li><a href="#1.14">1.14 Can I use TLS and the STARTTLS
        facility?</a></li>

        <li><a href="#1.15">1.15 Can I use CRAM-MD5 authentication?</a></li>

        <li><a href="#1.16">1.16 Can I use APOP authentication?</a></li>

        <li><a href="#1.17">1.17 Can I use Kerberos V5?</a></li>

        <li><a href="#1.18">1.18 Can I use PAM for plaintext
        passwords?</a></li>

        <li><a href="#1.19">1.19 Can I use Kerberos 5 for plaintext
        passwords?</a></li>

        <li><a href="#1.20">1.20 Can I use AFS for plaintext
        passwords?</a></li>

        <li><a href="#1.21">1.21 Can I use DCE for plaintext
        passwords?</a></li>

        <li><a href="#1.22">1.22 Can I use the CRAM-MD5 database for
        plaintext passwords?</a></li>

        <li><a href="#1.23">1.23 Can I disable plaintext passwords?</a></li>

        <li><a href="#1.24">1.24 Can I disable plaintext passwords on
        unencrypted sessions, but allow them on encrypted sessions?</a></li>

        <li><a href="#1.25">1.25 Can I use virtual hosts?</a></li>

        <li><a href="#1.26">1.26 Can I use RPOP authentication?</a></li>

        <li><a href="#1.27">1.27 Can I use Kerberos V4?</a></li>

        <li><a href="#1.28">1.28 Is there support for S/Key or OTP?</a></li>

        <li><a href="#1.29">1.29 Is there support for NTLM or SPA?</a></li>

        <li><a href="#1.30">1.30 Is there support for mh?</a></li>

        <li><a href="#1.31">1.31 Is there support for qmail and the maildir
        format?</a></li>

        <li><a href="#1.32">1.32 Is there support for the Cyrus mailbox
        format?</a></li>

        <li><a href="#1.33">1.33 Is this software Y2K compliant?</a></li>
      </ul>
    </li>

    <li>
      <a href="#requirements">2. What Do I Need to Build This Software?</a>

      <ul>
        <li><a href="#2.1">2.1 What do I need to build this software with SSL
        on UNIX?</a></li>

        <li><a href="#2.2">2.2 What do I need to build this software with
        Kerberos V on UNIX?</a></li>

        <li><a href="#2.3">2.3 What do I need to use a C++ compiler with this
        software to build my own application?</a></li>

        <li><a href="#2.4">2.4 What do I need to build this software on
        Windows?</a></li>

        <li><a href="#2.5">2.5 What do I need to build this software on
        DOS?</a></li>

        <li><a href="#2.6">2.6 Can't I use Borland C to build this software
        on the PC?</a></li>

        <li><a href="#2.7">2.7 What do I need to build this software on the
        Mac?</a></li>

        <li><a href="#2.8">2.8 What do I need to build this software on
        VMS?</a></li>

        <li><a href="#2.9">2.9 What do I need to build this software on
        TOPS-20?</a></li>

        <li><a href="#2.10">2.10 What do I need to build this software on
        Amiga or OS/2?</a></li>

        <li><a href="#2.11">2.11 What do I need to build this software on
        Windows CE?</a></li>
      </ul>
    </li>

    <li>
      <a href="#build">3. Build and Configuration Questions</a>

      <ul>
        <li><a href="#3.1">3.1 How do I configure the IMAP and POP servers on
        UNIX?</a></li>

        <li><a href="#3.2">3.2 I built and installed the servers according to
        the BUILD instructions. It can't be that easy. Don't I need to write
        a config file?</a></li>

        <li><a href="#3.3">3.3 How do I make the IMAP and POP servers look
        for INBOX at some place other than the mail spool directory?</a></li>

        <li><a href="#3.4">3.4 How do I make the IMAP server look for
        secondary folders at some place other than the user's home
        directory?</a></li>

        <li><a href="#3.5">3.5 How do I configure SSL?</a></li>

        <li><a href="#3.6">3.6 How do I configure TLS and the STARTTLS
        facility?</a></li>

        <li><a href="#3.7">3.7 How do I build/install OpenSSL and
        obtain/create certificates for use with SSL?</a></li>

        <li><a href="#3.8">3.8 How do I configure CRAM-MD5
        authentication?</a></li>

        <li><a href="#3.9">3.9 How do I configure APOP
        authentication?</a></li>

        <li><a href="#3.10">3.10 How do I configure Kerberos V5?</a></li>

        <li><a href="#3.11">3.11 How do I configure PAM for plaintext
        passwords?</a></li>

        <li><a href="#3.12">3.12 It looks like all I have to do to make the
        server use Kerberos is to build with PAM on my Linux system, and set
        it up in PAM for Kerberos passwords. Right?</a></li>

        <li><a href="#3.13">3.13 How do I configure Kerberos 5 for plaintext
        passwords?</a></li>

        <li><a href="#3.14">3.14 How do I configure AFS for plaintext
        passwords?</a></li>

        <li><a href="#3.15">3.15 How do I configure DCE for plaintext
        passwords?</a></li>

        <li><a href="#3.16">3.16 How do I configure the CRAM-MD5 database for
        plaintext passwords?</a></li>

        <li><a href="#3.17">3.17 How do I disable plaintext
        passwords?</a></li>

        <li><a href="#3.18">3.18 How do I disable plaintext passwords on
        unencrypted sessions, but allow them in SSL or TLS sessions?</a></li>

        <li><a href="#3.19">3.19 How do I configure virtual hosts?</a></li>

        <li>
          <a href="#3.20">3.20 Why do I get compiler warning messages such
          as:

          <ul>
            <li>passing arg 3 of `scandir' from incompatible pointer
            type</li>

            <li>Pointers are not assignment-compatible.</li>

            <li>Argument #4 is not the correct type.</li>
          </ul>during the build?</a>
        </li>

        <li>
          <a href="#3.21">3.21 Why do I get compiler warning messages such
          as

          <ul>
            <li>Operation between types "void(*)(int)" and "void*" is not
            allowed.</li>

            <li>Function argument assignment between types "void*" and
            "void(*)(int)" is not allowed.</li>

            <li>Pointers are not assignment-compatible.</li>

            <li>Argument #5 is not the correct type.</li>
          </ul>during the build?</a>
        </li>

        <li>
          <a href="#3.22">3.22 Why do I get linker warning messages such
          as:

          <ul>
            <li>mtest.c:515: the `gets' function is dangerous and should not
            be used.</li>
          </ul>during the build? Isn't this a security bug?</a>
        </li>

        <li>
          <a href="#3.23">3.23 Why do I get linker warning messages such
          as:</a>

          <ul>
            <li>auth_ssl.c:92: the `tmpnam' function is dangerous and should
            not be used.</li>
          </ul>during the build? Isn't this a security bug?
        </li>

        <li><a href="#3.24">3.24 OK, suppose I see a warning message about a
        function being "dangerous and should not be used" for something other
        than this gets() or tmpnam() call?</a></li>
      </ul>
    </li>

    <li>
      <a href="#operation">4. Operational Questions</a>

      <ul>
        <li><a href="#4.1">4.1 How can I enable anonymous IMAP
        logins?</a></li>

        <li><a href="#4.2">4.2 How do I set up an alert message that each
        IMAP user will see?</a></li>

        <li><a href="#4.3">4.3 How does the c-client library choose which of
        its several mechanisms to use to establish an IMAP connection to the
        server? I noticed that it can connect on port 143, port 993, via rsh,
        and via ssh.</a></li>

        <li><a href="#4.4">4.4 I am using a TLS-capable IMAP server, so I
        don't need to use /ssl to get encryption. However, I want to be
        certain that my session is TLS encrypted before I send my password.
        How to I do this?</a></li>

        <li><a href="#4.5">4.5 How do I use one of the alternative formats
        described in the formats.txt document? In particular, I hear that mbx
        format will give me better performance and allow shared
        access.</a></li>

        <li><a href="#4.6">4.6 How do I set up shared mailboxes?</a></li>

        <li><a href="#4.7">4.7 How can I make the server syslogs go to
        someplace other than the mail syslog?</a></li>
      </ul>
    </li>

    <li>
      <a href="#security">5. Security Questions</a>

      <ul>
        <li><a href="#5.1">5.1 I see that the IMAP server allows access to
        arbitary files on the system, including /etc/passwd! How do I disable
        this?</a></li>

        <li><a href="#5.2">5.2 I've heard that IMAP servers are insecure. Is
        this true?</a></li>

        <li><a href="#5.3">5.3 How do I know that I have the most secure
        version of the server?</a></li>

        <li><a href="#5.4">5.4 I see all these strcpy() and sprintf() calls,
        those are unsafe, aren't they?</a></li>

        <li><a href="#5.5">5.5 Those /tmp lock files are protected 666, is
        that really right?</a></li>
      </ul>
    </li>

    <li>
      <a href="#strange">6. <i>Why Did You Do This Strange Thing?</i>
      Questions</a>

      <ul>
        <li><a href="#6.1">6.1 Why don't you use GNU autoconfig / automake /
        autoblurdybloop?</a></li>

        <li><a href="#6.2">6.2 Why do you insist upon a build with -g?
        Doesn't it waste disk and memory space?</a></li>

        <li><a href="#6.3">6.3 Why don't you make c-client a shared
        library?</a></li>

        <li><a href="#6.4">6.4 Why don't you use iconv() for
        internationalization support?</a></li>

        <li><a href="#6.5">6.5 Why is the IMAP server connected to the home
        directory by default?</a></li>

        <li><a href="#6.6">6.6 I have a Windows system. Why isn't the server
        plug and play for me?</a></li>

        <li><a href="#6.7">6.7 I looked at the UNIX SSL code and saw that you
        have the SSL data payload size set to 8192 bytes. SSL allows 16K; why
        aren't you using the full size?</a></li>

        <li><a href="#6.8">6.8 Why is an mh format INBOX called #mhinbox
        instead of just INBOX?</a></li>

        <li><a href="#6.9">6.9 Why don't you support the maildir
        format?</a></li>

        <li><a href="#6.10">6.10 Why don't you support the Cyrus
        format?</a></li>

        <li><a href="#6.11">6.11 Why is it creating extra forks on my SVR4
        system?</a></li>

        <li><a href="#6.12">6.12 Why are you so fussy about the date/time
        format in the internal <code>"From&nbsp;"</code> line in traditional
        UNIX mailbox files? My other mail program just considers every line
        that starts with <code>"From&nbsp;"</code> to be the start of the
        message.</a></li>

        <li><a href="#6.13">6.13 Why is traditional UNIX format the default
        format?</a></li>

        <li><a href="#6.14">6.14 Why do you write this "DON'T DELETE THIS
        MESSAGE -- FOLDER INTERNAL DATA" message at the start of traditional
        UNIX and MMDF format mailboxes?</a></li>

        <li><a href="#6.15">6.15 Why don't you stash the mailbox metadata in
        the first real message of the mailbox instead of writing this fake
        FOLDER INTERNAL DATA message?</a></li>

        <li><a href="#6.16">6.16 Why aren't "dual-use" mailboxes the
        default?</a></li>

        <li><a href="#6.17">6.17 Why do you use ucbcc to build on
        Solaris?</a></li>

        <li><a href="#6.18">6.18 Why should I care about some old system with
        BSD libraries? cc is the right thing on my Solaris system!</a></li>

        <li><a href="#6.19">6.19 Why do you insist upon writing .lock files
        in the spool directory?</a></li>

        <li><a href="#6.20">6.20 Why should I care about compatibility with
        the past?</a></li>
      </ul>
    </li>

    <li>
      <a href="#problems">7. Problems and Annoyances</a>

      <ul>
        <li><a href="#7.1">7.1 Help! My INBOX is empty! What happened to my
        messages?</a></li>

        <li><a href="#7.2">7.2 Help! All my messages in a non-INBOX mailbox
        have been concatenated into one message which claims to be from me
        and has a subject of the file name of the mailbox! What's going
        on?</a></li>

        <li>
          <a href="#7.3">7.3 Why do I get the message:

          <ul>
            <li>CREATE failed: Can't create mailbox node xxxxxxxxx: File
            exists</li>
          </ul>and how do I fix it?</a>
        </li>

        <li><a href="#7.4">7.4 Why can't I log in to the server? The user
        name and password are right!</a></li>

        <li><a href="#7.5">7.5 Help! My load average is soaring and I see
        hundreds of POP and IMAP servers, many logged in as the same
        user!</a></li>

        <li><a href="#7.6">7.6 Why does mail disappear even though I set
        "keep mail on server"?</a></li>

        <li>
          <a href="#7.7">7.7 Why do I get the message

          <ul>
            <li>Moved ##### bytes of new mail to /home/user/mbox from
            /var/spool/mail/user</li>
          </ul>and why did this happen?</a>
        </li>

        <li><a href="#7.8">7.8 Why isn't it showing the local host name as a
        fully-qualified domain name?</a></li>

        <li><a href="#7.9">7.9 Why is the local host name in the
        From/Sender/Message-ID headers of outgoing mail not coming out as a
        fully-qualified domain name?</a></li>

        <li>
          <a href="#7.10">7.10 What does the message:

          <ul>
            <li>Mailbox vulnerable - directory /var/spool/mail must have 1777
            protection</li>
          </ul>mean? How can I fix this?</a>
        </li>

        <li>
          <a href="#7.11">7.11 What does the message:

          <ul>
            <li>Mailbox is open by another process, access is readonly</li>
          </ul>mean? How do I fix this?</a>
        </li>

        <li>
          <a href="#7.12">7.12 What does the message:

          <ul>
            <li>Can't get write access to mailbox, access is readonly</li>
          </ul>mean?</a>
        </li>

        <li><a href="#7.13">7.13 I set my POP3 client to "delete messages
        from server" but they never get deleted. What is wrong?</a></li>

        <li>
          <a href="#7.14">7.14 What do messages such as:

          <ul>
            <li>Message ... UID ... already has UID ...</li>

            <li>Message ... UID ... less than ...</li>

            <li>Message ... UID ... greater than last ...</li>

            <li>Invalid UID ... in message ..., rebuilding UIDs</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.15">7.15 What do the error messages:

          <ul>
            <li>Unable to read internal header at ...</li>

            <li>Unable to find CRLF at ...</li>

            <li>Unable to parse internal header at ...</li>

            <li>Unable to parse message date at ...</li>

            <li>Unable to parse message flags at ...</li>

            <li>Unable to parse message UID at ...</li>

            <li>Unable to parse message size at ...</li>

            <li>Last message (at ... ) runs past end of file ...</li>
          </ul>mean? I am using mbx format.</a>
        </li>

        <li>
          <a href="#7.16">7.16 What do the syslog messages:

          <ul>
            <li>imap/tcp server failing (looping)</li>

            <li>pop3/tcp server failing (looping)</li>
          </ul>mean? When it happens, the listed service shuts down. How can
          I fix this?</a>
        </li>

        <li>
          <a href="#7.17">7.17 What does the syslog message:

          <ul>
            <li>Mailbox lock file /tmp/.600.1df3 open failure: Permission
            denied</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.18">7.18 What do the syslog messages:

          <ul>
            <li>Command stream end of file, while reading line user=...
            host=...</li>

            <li>Command stream end of file, while reading char user=...
            host=...</li>

            <li>Command stream end of file, while writing text user=...
            host=...</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.19">7.19 Why did my POP or IMAP session suddenly
          disconnect? The syslog has the message:

          <ul>
            <li>Killed (lost mailbox lock) user=... host=...</li>
          </ul></a>
        </li>

        <li><a href="#7.20">7.20 Why does my IMAP client show all the files
        on the system, recursively from the UNIX root directory?</a></li>

        <li><a href="#7.21">7.21 Why does my IMAP client show all of my
        files, recursively from my UNIX home directory?</a></li>

        <li><a href="#7.22">7.22 Why does my IMAP client show that I have
        mailboxes named "#mhinbox", "#mh", "#shared", "#ftp", "#news", and
        "#public"?</a></li>

        <li><a href="#7.23">7.23 Why does my IMAP client show all my files in
        my home directory?</a></li>

        <li><a href="#7.24">7.24 Why is there a long delay before I get
        connected to the IMAP or POP server, no matter what client I
        use?</a></li>

        <li><a href="#7.25">7.25 Why is there a long delay in Pine or any
        other c-client based application call before I get connected to the
        IMAP server? The hang seems to be in the c-client mail_open() call. I
        don't have this problem with any other IMAP client. There is no delay
        connecting to a POP3 or NNTP server with mail_open().</a></li>

        <li><a href="#7.26">7.26 Why does a message sometimes get split into
        two or more messages on my SUN system?</a></li>

        <li>
          <a href="#7.27">7.27 Why did my POP or IMAP session suddenly
          disconnect? The syslog has the message:

          <ul>
            <li>Autologout user=&lt;...my user name...&gt; host=&lt;...my
            imap server...&gt;</li>
          </ul></a>
        </li>

        <li>
          <a href="#7.28">7.28 What does the UNIX error message:

          <ul>
            <li>TLS/SSL failure: myserver: SSL negotiation failed</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.29">7.29 What does the PC error message:

          <ul>
            <li>TLS/SSL failure: myserver: Unexpected TCP input
            disconnect</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.30">7.30 What does the error message:

          <ul>
            <li>TLS/SSL failure: myserver: Server name does not match
            certificate</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.31">7.31 What does the UNIX error message:

          <ul>
            <li>TLS/SSL failure: myserver: self-signed certificate</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.32">7.32 What does the PC error message

          <ul>
            <li>TLS/SSL failure: myserver: Self-signed certificate or
            untrusted authority</li>
          </ul>mean?</a>
        </li>

        <li>
          <a href="#7.33">7.33 What does the UNIX error message:

          <ul>
            <li>TLS/SSL failure: myserver: unable to get local issuer
            certificate</li>
          </ul>mean?</a>
        </li>

        <li><a href="#7.34">7.34 Why does reading certain messages hang when
        using Netscape? It works fine with Pine!</a></li>

        <li><a href="#7.35">7.35 Why does Netscape say that there's a problem
        with the IMAP server and that I should "Contact your mail server
        administrator."?</a></li>

        <li><a href="#7.36">7.36 Why is one user creating huge numbers of
        IMAP or POP server sessions?</a></li>

        <li><a href="#7.37">7.37 Why don't I get any new mail notifications
        from Outlook Express or Outlook after a while?</a></li>

        <li><a href="#7.38">7.38 Why don't I get any new mail notifications
        from Entourage?</a></li>

        <li><a href="#7.39">7.39 Why doesn't Entourage work at all?</a></li>

        <li><a href="#7.40">7.40 Why doesn't Netscape Notify (NSNOTIFY.EXE)
        work at all?</a></li>

        <li><a href="#7.41">7.41 Why can't I connect via SSL to Eudora? It
        says the connection has been broken, and in the server syslogs I see
        "Command stream end of file".</a></li>

        <li><a href="#7.42">7.42 Sheesh. Aren't there <i>any</i> good IMAP
        clients out there?</a></li>

        <li>
          <a href="#7.43">7.43 But wait! PC Pine (or other PC program build
          with c-client) crashes with the message

          <ul>
            <li>incomplete SecBuffer exceeds maximum buffer size</li>
          </ul>when I use SSL connections. This is a bug in c-client, right?</a>
        </li>

        <li><a href="#7.44">7.44 My qpopper users keep on getting the DON'T
        DELETE THIS MESSAGE -- FOLDER INTERNAL DATA if they also use Pine or
        IMAP. How can I fix this?</a></li>

        <li><a href="#7.45">7.45 Help! I installed the servers but I can't
        connect to them from my client!</a></li>

        <li>
          <a href="#7.46">7.46 Why do I get the message

          <ul>
            <li>Can not authenticate to SMTP server: 421 SMTP connection went
            away!</li>
          </ul>and why did this happen? There was also something about

          <ul>
            <li>SECURITY PROBLEM: insecure server advertised AUTH=PLAIN</li>
          </ul></a>
        </li>

        <li>
          <a href="#7.47">7.47 Why do I get the message

          <ul>
            <li>SMTP Authentication cancelled</li>
          </ul>and why did this happen? There was also something about

          <ul>
            <li>SECURITY PROBLEM: insecure server advertised AUTH=PLAIN</li>
          </ul></a>
        </li>

        <li>
          <a href="#7.48">7.48 Why do I get the message

          <ul>
            <li>Invalid base64 string</li>
          </ul>when I try to authenticate to a Cyrus server?
        </li></a>
      </ul>
    </li>

    <li>
      <a href="#additional">8. Where to Go For Additional Information</a>

      <ul>
        <li><a href="#8.1">8.1 Where can I go to ask questions?</a></li>

        <li><a href="#8.2">8.2 I have some ideas for enhancements to IMAP.
        Where should I go?</a></li>

        <li><a href="#8.3">8.3 Where can I read more about IMAP and other
        email protocols?</a></li>

        <li><a href="#8.4">8.4 Where can I find out more about setting up and
        administering an IMAP server?</a></li>
      </ul>
    </li>
  </ul><!--=======START BODY-->
  <hr>

  <h2><a name="general">1. General/Software Feature Questions</a></h2>
  <hr>

  <p><a name="1.1"><strong>1.1 Can I set up a POP or IMAP server on
     UNIX/Linux/OSF/etc.?</strong></a></p>

  <dl>
    <dd>Yes. Refer to the UNIX specific notes in files CONFIG and BUILD.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.2"><strong>1.2 I am currently using qpopper as my POP3 server on
     UNIX. Do I need to replace it with ipop3d in order to run
     imapd?</strong></a></p>

  <dl>
    <dd>
      Not necessarily.

      <p>Although ipop3d interoperates with imapd better than qpopper, imapd
      and qpopper will work together. The few qpopper/imapd interoperability
      issues mostly affect users who use both IMAP and POP3 clients; those
      users would probably be better served if their POP3 server is
      ipop3d.</p>

      <p>If you are happy with qpopper and just want to add imapd, you should
      do that, and defer a decision on changing qpopper to ipop3d. That way,
      you can get comfortable with imapd's performance, without changing
      anything for your qpopper users.</p>

      <p>Many sites have subsequently decided to change from qpopper to
      ipop3d in order to get better POP3/IMAP interoperability. If you need
      to do this, you'll know. There also seems to be a way to make qpopper
      work better with imapd; see the answer to the <a href="#7.44">My
      qpopper users keep on getting the DON'T DELETE THIS MESSAGE -- FOLDER
      INTERNAL DATA if they also use Pine or IMAP. How can I fix this?</a>
      question.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.3"><strong>1.3 Can I set up a POP or IMAP server on Windows XP,
     2000, NT, Me, 98, or 95?</strong></a></p>

  <dl>
    <dd>
      Yes. Refer to the NT specific notes in files CONFIG and BUILD. Also,
      for DOS-based versions of Windows (Windows Me, 98, and 95) you *must*
      set up CRAM-MD5 authentication, as described in md5.txt.

      <p>There is no file access control on Windows 9x or Me, so you probably
      will have to do modifications to env_unix.c to prevent people from
      hacking others' mail.</p>

      <p>Note, however, that the server is not plug and play the way it is
      for UNIX.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.4"><strong>1.4 Can I set up a POP or IMAP server on Windows 3.1 or
     DOS?</strong></a><br>
  <a name="1.5"><strong>1.5 Can I set up a POP or IMAP server on
     Macintosh?</strong></a><br>
  <a name="1.6"><strong>1.6 Can I set up a POP or IMAP server on
     VAX/VMS?</strong></a></p>

  <dl>
    <dd>Yes, it's just a small matter of programming.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.7"><strong>1.7 Can I set up a POP or IMAP server on
     TOPS-20?</strong></a></p>

  <dl>
    <dd>
      You have a TOPS-20 system? Cool.

      <p>If IMAP2 (RFC 1176) is good enough for you, you can use MAPSER which
      is about the ultimate gonzo pure TOPS-20 extended addressing assembly
      language program. Unfortunately, IMAP2 is barely good enough for Pine
      these days, and most other IMAP clients won't work with IMAP2 at all.
      Maybe someone will hack MAPSER to do IMAP4rev1 some day.</p>

      <p>We don't know if anyone wrote a POP3 server for TOPS-20. There
      definitely was a POP2 server once upon a time.</p>

      <p>Or you can port the POP and IMAP server from this IMAP toolkit to
      it. All that you need for a first stab is to port the MTX driver.
      That'll probably be just a couple of hours of hacking.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.8"><strong>1.8 Are hierarchical mailboxes
     supported?</strong></a><br>
  <a name="1.9"><strong>1.9 Are "dual-use" mailboxes
     supported?</strong></a><br>
  <a name="1.10"><strong>1.10 Can I have a mailbox that has both messages and
     sub-mailboxes?</strong></a></p>

  <dl>
    <dd>
      Yes. However, there is one important caveat.

      <p>Some mailbox formats, including the default which is the traditional
      UNIX mailbox format, are stored as a single file containing all the
      messages. UNIX does not permit a name in the filesystem to be both a
      file and a directory; consequently you can not have a sub-mailbox
      within a mailbox that is in one of these formats.</p>

      <p>This is not a limitation of the software; this is a limitation of
      UNIX. For example, there are mailbox formats in which the name is a
      directory and each message is a file within that directory; these
      formats support sub-mailboxes within such mailboxes. However, for
      technical reasons, the "flat file" formats are generally preferred
      since they perform better. Read imap-2007/docs/formats.txt for more
      information on this topic.</p>

      <p>It is always permissible to create a directory that is not a
      mailbox, and have sub-mailboxes under it. The easiest way to create a
      directory is to create a new mailbox inside a directory that doesn't
      already exist. For example, if you create "Mail/testbox" on UNIX, the
      directory "Mail/" will automatically be created and then the mailbox
      "testbox" will be created as a sub-mailbox of "Mail/".</p>

      <p>It is also possible to create the name "Mail/" directly. Check the
      documentation for your client software to see how to do this with that
      software.</p>

      <p>Of course, on Windows systems you would use "\" instead of "/".</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.11"><strong>1.11 What is the difference between "mailbox" and
     "folder"?</strong></a></p>

  <dl>
    <dd>
      The term "mailbox" is IMAP-speak for what a lot of software calls a
      "folder" or a "mail folder". However, "folder" is often used in other
      contexts to refer to a directory, for example, in the graphic user
      interface on both Windows and Macintosh.

      <p>A "mailbox" is specifically defined as a named object that contains
      messages. It is not required to be capable of containing other types of
      objects including other mailboxes; although some mailbox formats will
      permit this.</p>

      <p>In IMAP-speak, a mailbox which can not contain other mailboxes is
      called a "no-inferiors mailbox". Similarly, a directory which can not
      contain messages is not a mailbox and is called a "no-select name".</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.12"><strong>1.12 What is the status of
     internationalization?</strong></a></p>

  <dl>
    <dd>
      The IMAP toolkit is partially internationalized and multilingualized.

      <p>Searching is supported in the following charsets: US-ASCII, UTF-8,
      ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6,
      ISO-8859-7, ISO-8859-8, ISO-8859-9, ISO-8859-10, ISO-8859-11,
      ISO-8859-13, ISO-8859-14, ISO-8859-15, ISO-8859-16, KOI8-R, KOI8-U
      (alias KOI8-RU), TIS-620, VISCII, ISO-2022-JP, ISO-2022-KR,
      ISO-2022-CN, ISO-2022-JP-1, ISO-2022-JP-2, GB2312 (alias CN-GB),
      CN-GB-12345, BIG5 (alias CN-BIG5), EUC-JP, EUC-KR, Shift_JIS,
      Shift-JIS, KS_C_5601-1987, KS_C_5601-1992, WINDOWS_874, WINDOWS-1250,
      WINDOWS-1251, WINDOWS-1252, WINDOWS-1253, WINDOWS-1254, WINDOWS-1255,
      WINDOWS-1256, WINDOWS-1257, WINDOWS-1258.</p>

      <p>All ISO-2022-?? charsets are treated identically, and support ASCII,
      JIS Roman, hankaku katakana, ISO-8859-[1 - 10], TIS, GB 2312, JIS X
      0208, JIS X 0212, KSC 5601, and planes 1 and 2 of CNS 11643.</p>

      <p>EUC-JP includes support for JIS X 0212 and hankaku katakana.</p>

      <p>c-client library support also exists to convert text in any of the
      above charsets into Unicode, including headers with MIME
      encoded-words.</p>

      <p>There is no support for localization (e.g. non-English error
      messages) at the present time, but such support is planned.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.13"><strong>1.13 Can I use SSL?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.5">How do I configure SSL?</a>
    question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.14"><strong>1.14 Can I use TLS and the STARTTLS
     facility?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.6">How do I configure TLS and
    the STARTTLS facility?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.15"><strong>1.15 Can I use CRAM-MD5
     authentication?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.8">How do I configure CRAM-MD5
    authentication?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.16"><strong>1.16 Can I use APOP authentication?</strong></a></p>

  <dl>
    <dd>
      Yes. See the <a href="#3.9">How do I configure APOP authentication?</a>
      question.

      <p>Note that there is no client support for APOP authentication.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.17"><strong>1.17 Can I use Kerberos V5?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.10">How do I configure
    Kerberos V5?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.18"><strong>1.18 Can I use PAM for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.11">How do I configure PAM for
    plaintext passwords?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.19"><strong>1.19 Can I use Kerberos 5 for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.13">How do I configure
    Kerberos 5 for plaintext passwords?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.20"><strong>1.20 Can I use AFS for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.14">How do I configure AFS for
    plaintext passwords?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.21"><strong>1.21 Can I use DCE for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.15">How do I configure DCE for
    plaintext passwords?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.22"><strong>1.22 Can I use the CRAM-MD5 database for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.16">How do I configure the
    CRAM-MD5 database for plaintext passwords?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.23"><strong>1.23 Can I disable plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.17">How do I disable plaintext
    passwords?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.24"><strong>1.24 Can I disable plaintext passwords on unencrypted
     sessions, but allow them on encrypted sessions?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.18">How do I disable plaintext
    passwords on unencrypted sessions, but allow them in SSL or TLS
    sessions?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.25"><strong>1.25 Can I use virtual hosts?</strong></a></p>

  <dl>
    <dd>Yes. See the answer to the <a href="#3.19">How do I configure virtual
    hosts?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.26"><strong>1.26 Can I use RPOP authentication?</strong></a></p>

  <dl>
    <dd>There is no support for RPOP authentication.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.27"><strong>1.27 Can I use Kerberos V4?</strong></a></p>

  <dl>
    <dd>
      Kerberos V4 is not supported. Kerberos V4 client-only contributed code
      is available in
      <pre>
<a href=
"ftp://ftp.cac.washington.edu/mail/kerberos4-patches.tar.Z">ftp://ftp.cac.washington.edu/mail/kerberos4-patches.tar.Z
</a>
</pre>This is a patchkit which must be applied to the IMAP toolkit according
to the instructions in the patchkit's README. We can not promise that this
code works.
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.28"><strong>1.28 Is there support for S/Key or
     OTP?</strong></a></p>

  <dl>
    <dd>There is currently no support for S/Key or OTP. There may be an OTP
    SASL authenticator available from third parties.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.29"><strong>1.29 Is there support for NTLM or
     SPA?</strong></a></p>

  <dl>
    <dd>
      There is currently no support for NTLM or SPA, nor are there any plans
      to add such support. In general, I avoid vendor-specific mechanisms. I
      also believe that these mechanisms are being deprecated by their
      vendor.

      <p>There may be an NTLM SASL authenticator available from third
      parties.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.30"><strong>1.30 Is there support for mh?</strong></a></p>

  <dl>
    <dd>
      Yes, but only as a legacy format. Your mh format INBOX is accessed by
      the name "#mhinbox", and all other mh format mailboxes are accessed by
      prefixing "#mh/" to the name, e.g. "#mh/foo". The mh support uses the
      "Path:" entry in your .mh_profile file to identify the root directory
      of your mh format mailboxes.

      <p>Non-legacy use of mh format is not encouraged. There is no support
      for permanent flags or unique identifiers; furthermore there are known
      severe performance problems with the mh format.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.31"><strong>1.31 Is there support for qmail and the maildir
     format?</strong></a></p>

  <dl>
    <dd>There is no support for qmail or the maildir format in our
    distribution, nor are there any plans to add such support. Maildir
    support may be available from third parties.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.32"><strong>1.32 Is there support for the Cyrus mailbox
     format?</strong></a></p>

  <dl>
    <dd>No.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="1.33"><strong>1.33 Is this software Y2K compliant?</strong></a></p>

  <dl>
    <dd>Please read the files Y2K and calendar.txt.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="requirements">2. What Do I Need to Build This Software?</a></h2>
  <hr>

  <p><a name="2.1"><strong>2.1 What do I need to build this software with SSL on
     UNIX?</strong></a></p>

  <dl>
    <dd>You need to build and install OpenSSL first.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.2"><strong>2.2 What do I need to build this software with Kerberos
     V on UNIX?</strong></a></p>

  <dl>
    <dd>You need to build and install MIT Kerberos first.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.3"><strong>2.3 What do I need to use a C++ compiler with this
     software to build my own application?</strong></a></p>

  <dl>
    <dd>
      If you are building an application using the c-client library, use the
      new c-client.h file instead of including the other include files. It
      seems that c-client.h should define away all the troublesome names that
      conflict with C++.

      <p>If you use gcc, you may need to use -fno-operator-names as well.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.4"><strong>2.4 What do I need to build this software on
     Windows?</strong></a></p>

  <dl>
    <dd>
      You need Microsoft Visual C++ 6.0, Visual C++ .NET, or Visual C# .NET
      (which you can buy from any computer store), along with the Microsoft
      Platform SDK (which you can download from Microsoft's web site).

      <p>You do not need to install the entire Platform SDK; it suffices to
      install just the Core SDK and the Internet Development SDK.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.5"><strong>2.5 What do I need to build this software on
     DOS?</strong></a></p>

  <dl>
    <dd>It's been several years since we last attempted to do this. At the
    time, we used Microsoft C.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.6"><strong>2.6 Can't I use Borland C to build this software on the
     PC?</strong></a></p>

  <dl>
    <dd>Probably not. If you know otherwise, please let us know.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.7"><strong>2.7 What do I need to build this software on the
     Mac?</strong></a></p>

  <dl>
    <dd>It has been several years since we last attempted to do this. At the
    time, we used Symantec THINK C; but today you'll need a C compiler which
    allows segments to be more than 32K.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.8"><strong>2.8 What do I need to build this software on
     VMS?</strong></a></p>

  <dl>
    <dd>You need the VMS C compiler, and either the Multinet or Netlib
    TCP.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.9"><strong>2.9 What do I need to build this software on
     TOPS-20?</strong></a></p>

  <dl>
    <dd>You need the TOPS-20 KCC compiler.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.10"><strong>2.10 What do I need to build this software on Amiga or
     OS/2?</strong></a></p>

  <dl>
    <dd>We don't know.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="2.11"><strong>2.11 What do I need to build this software on Windows
     CE?</strong></a></p>

  <dl>
    <dd>This port is incomplete. Someone needs to finish it.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="build">3. Build and Configuration Questions</a></h2>
  <hr>

  <p><a name="3.1"><strong>3.1 How do I configure the IMAP and POP servers on
     UNIX?</strong></a><br>
  <a name="3.2"><strong>3.2 I built and installed the servers according to the
     BUILD instructions. It can't be that easy. Don't I need to write a
     config file?</strong></a></p>

  <dl>
    <dd>
      For ordinary "vanilla" UNIX systems, this software is plug and play;
      just build it, install it, and you're done. If you have a modified
      system, then you may want to do additional work; most of this is to a
      single source code file (env_unix.c on UNIX systems). Read the file
      CONFIG for more details.

      <p>Yes, it's that easy. There are some additional options, such as SSL
      or Kerberos, which require additional steps to build. See the relevant
      questions below.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.3"><strong>3.3 How do I make the IMAP and POP servers look for
     INBOX at some place other than the mail spool
     directory?</strong></a><br>
  <a name="3.4"><strong>3.4 How do I make the IMAP server look for secondary
     folders at some place other than the user's home
     directory?</strong></a></p>

  <dl>
    <dd>Please read the file CONFIG for discussion of this and other
    issues.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.5"><strong>3.5 How do I configure SSL?</strong></a><br>
  <a name="3.6"><strong>3.6 How do I configure TLS and the STARTTLS
     facility?</strong></a></p>

  <dl>
    <dd>
      imap-2007 supports SSL and TLS client functionality on UNIX and 32-bit
      Windows for IMAP, POP3, SMTP, and NNTP; and SSL and TLS server
      functionality on UNIX for IMAP and POP3.

      <p>UNIX SSL build requires that a third-party software package,
      OpenSSL, be installed on the system first. Read imap-2007/docs/SSLBUILD
      for more information.</p>

      <p>SSL is supported via undocumented Microsoft interfaces in Windows 9x
      and NT4; and via standard interfaces in Windows 2000, Windows
      Millenium, and Windows XP.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.7"><strong>3.7 How do I build/install OpenSSL and obtain/create
     certificates for use with SSL?</strong></a></p>

  <dl>
    <dd>If you need help in doing this, try the contacts mentioned in the
    OpenSSL README. We do not offer support for OpenSSL or certificates.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.8"><strong>3.8 How do I configure CRAM-MD5
     authentication?</strong></a><br>
  <a name="3.9"><strong>3.9 How do I configure APOP
     authentication?</strong></a></p>

  <dl>
    <dd>
      CRAM-MD5 authentication is enabled in the IMAP and POP3 client code on
      all platforms. Read md5.txt to learn how to set up CRAM-MD5 and APOP
      authentication on UNIX and NT servers.

      <p>There is no support for APOP client authentication.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.10"><strong>3.10 How do I configure Kerberos V5?</strong></a></p>

  <dl>
    <dd>
      imap-2007 supports client and server functionality on UNIX and 32-bit
      Windows.

      <p>Kerberos V5 is supported by default in Windows 2000 builds:</p>
      <pre>
 nmake -f makefile.w2k
</pre>

      <p>Other builds require that a third-party Kerberos package, e.g. MIT
      Kerberos, be installed on the system first.</p>

      <p>To build with Kerberos V5 on UNIX, include EXTRAAUTHENTICATORS=gss
      in the make command line, e.g.</p>
      <pre>
 make lnp EXTRAAUTHENTICATORS=gss
</pre>

      <p>To build with Kerberos V5 on Windows 9x, Windows Millenium, and NT4,
      use the "makefile.ntk" file instead of "makefile.nt":</p>
      <pre>

 nmake -f makefile.ntk
</pre>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.11"><strong>3.11 How do I configure PAM for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>
      On Linux systems, use the lnp port, e.g.
      <pre>
 make lnp

</pre>On Solaris systems and other systems with defective PAM
implementations, build with PASSWDTYPE=pmb, e.g.
      <pre>
 make sol PASSWDTYPE=pmb
</pre>On all other systems, build with PASSWDTYPE=pam, e.g
      <pre>
 make foo PASSWDTYPE=pam
</pre>If you build with PASSWDTYPE=pam and authentication does not work, try
rebuilding (after a "make clean") with PASSWDTYPE=pmb.
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.12"><strong>3.12 It looks like all I have to do to make the server
     use Kerberos is to build with PAM on my Linux system, and set it up in
     PAM for Kerberos passwords. Right?</strong></a></p>

  <dl>
    <dd>
      Yes and no.

      <p>Doing this will make plaintext password authentication use the
      Kerberos password instead of the /etc/passwd password.</p>

      <p>However, this will NOT give you Kerberos-secure authentication. See
      the answer to the <a href="#3.10">How do I configure Kerberos V5?</a>
      question for how to build with Kerberos-secure authentication.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.13"><strong>3.13 How do I configure Kerberos 5 for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>
      Build with PASSWDTYPE=gss, e.g.
      <pre>
 make sol PASSWDTYPE=gss
</pre>However, this will NOT give you Kerberos-secure authentication. See the
answer to the <a href="#3.10">How do I configure Kerberos V5?</a> question
for how to build with Kerberos-secure authentication.
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.14"><strong>3.14 How do I configure AFS for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>
      Build with PASSWDTYPE=afs, e.g
      <pre>
 make sol PASSWDTYPE=afs

</pre>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.15"><strong>3.15 How do I configure DCE for plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>
      Build with PASSWDTYPE=dce, e.g
      <pre>
 make sol PASSWDTYPE=dce
</pre>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.16"><strong>3.16 How do I configure the CRAM-MD5 database for
     plaintext passwords?</strong></a></p>

  <dl>
    <dd>
      The CRAM-MD5 password database is automatically used for plaintext
      password if it exists.

      <p>Note that this is NOT CRAM-MD5-secure authentication. You probably
      want to consider disabling plaintext passwords for non-SSL/TLS
      sessions. See the next two questions.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.17"><strong>3.17 How do I disable plaintext
     passwords?</strong></a></p>

  <dl>
    <dd>
      Server-level plaintext passwords can be disabled by setting
      PASSWDTYPE=nul, e.g.
      <pre>
 make lnx EXTRAAUTHENTICATORS=gss PASSWDTYPE=nul
</pre>Note that you must have a CRAM-MD5 database installed or specify at
least one EXTRAAUTHENTICATOR, otherwise it will not be possible to log in to
the server.

      <p>When plaintext passwords are disabled, the IMAP server will
      advertise the LOGINDISABLED capability and the POP3 server will not
      advertise the USER capability.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>

  <p><a name="3.18"><strong>3.18 How do I disable plaintext passwords on
     unencrypted sessions, but allow them in SSL or TLS
     sessions?</strong></a></p>

  <dl>
    <dd>
      <p>Do not set PASSWDTYPE=nul or SSLTYPE=unix. Set SSLTYPE=nopwd
      instead, e.g.</p>
      <pre>
 make lnx SSLTYPE=nopwd
</pre>

      <p>When plaintext passwords are disabled, the IMAP server will
      advertise the LOGINDISABLED capability and the POP3 server will not
      advertise the USER capability.</p>

      <p>Plaintext passwords will always be enabled in SSL sessions; the IMAP
      server will not advertise the LOGINDISABLED capability and the POP3
      server will advertise the USER capability.</p>

      <p>If the client does a successful start-TLS in a non-SSL session,
      plaintext passwords will be enabled, and a new CAPABILITY or CAPA
      command (which is required after start-TLS) will show the effect as in
      SSL sessions.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.19"><strong>3.19 How do I configure virtual
     hosts?</strong></a></p>

  <dl>
    <dd>
      This is automatic, but with certain restrictions.

      <p>The most important one is that each virtual host must have its own
      IP address; otherwise the server has no way of knowing which virtual
      host is desired.</p>

      <p>As distributed, the software uses a global password file; hence user
      "fred" on one virtual host is "fred" on all virtual hosts. You may want
      to modify the checkpw() routine to implement some other policy (e.g.
      separate password files).</p>

      <p>Note that the security model assumes that all users have their own
      unique UNIX UID number. So if you use separate password files you
      should make certain that the UID numbers do not overlap between
      different files.</p>

      <p>More advanced virtual host support may be available as patches from
      third parties.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.20"><strong>3.20 Why do I get compiler warning messages such
     as:</strong></a></p>
  <pre>
 passing arg 3 of `scandir' from incompatible pointer type
 Pointers are not assignment-compatible.
 Argument #4 is not the correct type.

</pre>

  <p><strong>during the build?</strong></p>

  <dl>
    <dd>
      You can safely ignore these messages.

      <p>Over the years, the prototype for scandir() has changed, and thus is
      variant across different UNIX platforms. In particular, the definitions
      of the third argument (type select_t) and fourth argument (type
      compar_t) have changed over the years, the issue being whether or not
      the arguments to the functions pointed to by these function pointers
      are of type const or not.</p>

      <p>The way that c-client calls scandir() will tend to generate these
      compiler warnings on newer systems such as Linux; however, it will
      still build. The problem with fixing the call is that then it won't
      build on older systems.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.21"><strong>3.21 Why do I get compiler warning messages such
     as</strong></a></p>
  <pre>
 Operation between types "void(*)(int)" and "void*" is not allowed.
 Function argument assignment between types "void*" and "void(*)(int)" is not allowed.
 Pointers are not assignment-compatible.
 Argument #5 is not the correct type.
</pre>

  <p><strong>during the build?</strong></p>

  <dl>
    <dd>
      You can safely ignore these messages.

      <p>All known systems have no problem with casting a function pointer
      to/from a void* pointer, certain C compilers issue a compiler
      diagnostic because this facility is listed as a "Common extension" by
      the C standard:</p>
      <pre>
 K.5.7  Function pointer casts
  [#1] A pointer to an object or to void may be cast to a pointer
       to a function, allowing data to be invoked as a function (6.3.4).
  [#2] A pointer to a function may be cast to a pointer to an
       object or to void, allowing a function to be inspected or
       modified (for example, by a debugger) (6.3.4).

</pre>It may be just a "common extension", but this facility is relied upon
heavily by c-client.
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.22"><strong>3.22 Why do I get linker warning messages such
     as:</strong></a></p>
  <pre>
mtest.c:515: the `gets' function is dangerous and should not be used.
</pre>

  <p><strong>during the build? Isn't this a security bug?</strong></p>

  <dl>
    <dd>
      You can safely ignore this message.

      <p>Certain linkers, most notably on Linux, give this warning message.
      It is indeed true that the traditional gets() function is not a safe
      one.</p>

      <p>However, the mtest program is only a demonstration program, a model
      of a very basic application program using c-client. It is not something
      that you would install, much less run in any security-sensitive
      context.</p>

      <p>mtest has numerous other shortcuts that you wouldn't want to do in a
      real application program.</p>

      <p>The only "security bug" with mtest would be if it was run by some
      script in a security-sensitive context, but mtest isn't particularly
      useful for such purposes. If you wanted to write a script to automate
      some email task using c-client, you'd be better off using imapd instead
      of mtest.</p>

      <p>mtest only has two legitimate uses. It's a useful testbed for me
      when debugging new versions of c-client, and it's useful as a model for
      someone writing a simple c-client application to see how the various
      calls work.</p>

      <p>By the way, if you need a more advanced example of c-client
      programming than mtest (and you probably will), I recommend that you
      look at the source code for imapd and Pine.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.23"><strong>3.23 Why do I get linker warning messages such
     as:</strong></a></p>
  <pre>
 auth_ssl.c:92: the `tmpnam' function is dangerous and should not be used.
</pre>

  <p><strong>during the build? Isn't this a security bug?</strong></p>

  <dl>
    <dd>
      You can safely ignore this message.

      <p>Certain linkers, most notably on Linux, give this warning message,
      based upon two known issues with tmpnam():</p>

      <dl>
        <dd>there can be a buffer overflow if an inadequate buffer is
        allocated.</dd>

        <dd>there can be a timing race caused by certain incautious usage of
        the return value.</dd>
      </dl>

      <p>Neither of these issues applies in the particular use that is made
      of tmpnam(). More importantly, the tmpnam() call is never executed on
      Linux systems.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="3.24"><strong>3.24 OK, suppose I see a warning message about a
     function being "dangerous and should not be used" for something other
     than this gets() or tmpnam() call?</strong></a></p>

  <dl>
    <dd>Please forward the details for investigation.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="operation">4. Operational Questions</a></h2>
  <hr>

  <p><a name="4.1"><strong>4.1 How can I enable anonymous IMAP
     logins?</strong></a></p>

  <dl>
    <dd>Create the file /etc/anonymous.newsgroups. At the present time, this
    file should be empty. This will permit IMAP logins as anonymous as well
    as the ANONYMOUS SASL authenticator. Anonymous users have access to
    mailboxes in the #news., #ftp/, and #public/ namespaces only.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="4.2"><strong>4.2 How do I set up an alert message that each IMAP
     user will see?</strong></a></p>

  <dl>
    <dd>Create the file /etc/imapd.alert with the text of the message. This
    text should be kept to one line if possible. Note that this will cause an
    alert to every IMAP user every time they initiate an IMAP session, so it
    should only be used for critical messages.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="4.3"><strong>4.3 How does the c-client library choose which of its
     several mechanisms to use to establish an IMAP connection to the server?
     I noticed that it can connect on port 143, port 993, via rsh, and via
     ssh.</strong></a></p>

  <dl>
    <dd>
      c-client chooses how to establish an IMAP connection via the following
      rules:

      <ul>
        <li>If /ssl is specified, use an SSL connection. Fail otherwise.</li>

        <li>Else if client is a UNIX system and "ssh server exec /etc/rimapd"
        works, use that</li>

        <li>Else if /tryssl is specified and an SSL connection works, use
        that.</li>

        <li>Else if client is a UNIX system and "rsh server exec /etc/rimapd"
        works, use that.</li>

        <li>Else use a non-SSL connection.</li>
      </ul>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="4.4"><strong>4.4 I am using a TLS-capable IMAP server, so I don't
     need to use /ssl to get encryption. However, I want to be certain that
     my session is TLS encrypted before I send my password. How to I do
     this?</strong></a></p>

  <dl>
    <dd>Use the /tls option in the mailbox name. This will cause an error
    message and the connection to fail if the server does not negotiate
    STARTTLS.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="4.5"><strong>4.5 How do I use one of the alternative formats
     described in the formats.txt document? In particular, I hear that mbx
     format will give me better performance and allow shared
     access.</strong></a></p>

  <dl>
    <dd>
      The rumors about mbx format being preferred are true. It is faster than
      the traditional UNIX mailbox format and permits shared access.

      <p>However, and this is <em>very important</em>, note that using an
      alternative mailbox format is an advanced facility, and only expert
      users should undertake it. If you don't understand any of the following
      notes, you may not be enough of an expert yet, and are probably better
      off not going this route until you are more comfortable with your
      understanding.</p>

      <p>Some of the formats, including mbx, are only supported by the
      software based on the c-client library, and are not recognized by other
      mailbox programs. The "vi" editor will corrupt any mbx format mailbox
      that it encounters.</p>

      <p>Another problem is that the certain formats, including mbx, use
      advanced file access and locking techniques that do <em>not</em> work
      reliably with NFS. NFS is not a real filesystem. Use IMAP instead of
      NFS for distributed access.</p>

      <p>Each of the following steps are in escalating order of involvement.
      The further you go down this list, the more deeply committed you
      become:</p>

      <ul>
        <li>The simplest way to create a mbx-format mailbox is to prefix the
        name with "#driver.mbx/" when creating a mailbox through c-client.
        For example, if you create "#driver.mbx/foo", the mailbox "foo" will
        be created in mbx format. Only use "#driver.mbx/" when creating the
        mailbox. At all other times, just use the name ("foo" in this
        example); the software will automatically select the driver for mbx
        whenever that mailbox is accessed without you doing anything
        else.</li>

        <li>You can use the "mailutil copy" command to copy an existing
        mailbox to a new mailbox in mbx format. Read the man page provided
        with the mailutil program for details.</li>

        <li>If you create an mbx-format INBOX, by creating
        "#driver.mbx/INBOX" (note that "INBOX" must be all uppercase), then
        subsequent access to INBOX by any c-client based application will use
        the mbx-format INBOX. Any mail delivered to the traditional format
        mailbox in the spool directory (e.g. /var/spool/mail/$USER) will
        automatically be copied into the mbx-format INBOX and the spool
        directory copy removed.</li>

        <li>You can cause any newly-created mailboxes to be in mbx-format by
        default by changing the definition of CREATEPROTO=unixproto to be
        CREATEPROTO=mbxproto in src/osdep/unix/Makefile, then rebuilding the
        IMAP toolkit (do a "make clean" first). Do not change EMPTYPROTO,
        since mbx format mailboxes are never a zero-byte file. If you use
        Pine or the imap-utils, you should probably also rebuild them with
        the new IMAP toolkit too.</li>

        <li>You can deliver directly to the mbx-format INBOX by use of the
        tmail or dmail programs. tmail is for direct invocation from sendmail
        (or whatever MTA program you use); dmail is for calls from procmail.
        Both of these programs have man pages which must be read carefully
        before making this change.</li>
      </ul>

      <p>Most other servers (e.g. Cyrus) require use of a non-standard
      format. A full-fledged format conversion is not significantly different
      from what you have to do with other servers. The difference, which
      makes format conversion procedures somewhat more complicated with this
      server, is that there is no "all or nothing" requirement with this
      server. There are many points in between. A format conversion can be
      anything from a single mailbox or single user, to systemwide.</p>

      <p>This is good in that you can decide how far to go, or do the steps
      incrementally as you become more comfortable with the result. On the
      other hand, there's no "One True Way" which can be boiled down to a
      simple set of pedagogical instructions.</p>

      <p>A number of sites have done full-fledged format conversions, and are
      reportedly quite happy with the results. Feel free to ask in the
      comp.mail.imap newsgroup or the imap-uw mailing list for advice or
      help.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="4.6"><strong>4.6 How do I set up shared mailboxes?</strong></a></p>

  <dl>
    <dd>
      At the simplest level, a shared mailbox is one which has UNIX file and
      directory protections which permit multiple users to access it. What
      this means is that your existing skills and tools to create and manage
      shared files on your UNIX system apply to shared mailboxes; e.g.
      <pre>
 chmod 666 mailbox
</pre>

      <p>You may want to consider the use of a mailbox format which permits
      multiple simultaneous read/write sessions, such as the mbx format. The
      traditional UNIX format only allows one read/write session to a
      mailbox at a time.</p>

      <p>An additional convenience item are three system directories, which
      can be set up for shared namespaces. These are: #ftp, #shared, and
      #public, and are defined by creating the associated UNIX users and home
      directories as described below.</p>

      <p>#ftp/ refers to the anonymous ftp filesystem exported by the ftp
      server, and is equivalent to the home directory for UNIX user "ftp".
      For example, #ftp/foo/bar refers to the file /foo/bar in the anonymous
      FTP filesystem, or ~ftp/foo/bar for normal users. Anonymous FTP files
      are available to anonymous IMAP logins. By default, newly-created files
      in #ftp/ are protected 644.</p>

      <p>#public/ refers to an IMAP toolkit convention called "public" files,
      and is equivalent to the home directory for UNIX user "imappublic". For
      example, #public/foo/bar refers to the file ~imappublic/foo/bar. Public
      files are available to anonymous IMAP logins. By default, newly-created
      files in #public are created with protection 0666.</p>

      <p>#shared/ refers to an IMAP toolkit convention called "shared" files,
      and is equivalent to the home directory for UNIX user "imapshared". For
      example, #shared/foo/bar refers to the file ~imapshared/foo/bar. Shared
      files are <em>not</em> available to anonymous IMAP logins. By default,
      newly-created files in #shared are created with protection 0660.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="4.7"><strong>4.7 How can I make the server syslogs go to someplace
     other than the mail syslog?</strong></a></p>

  <dl>
    <dd>
      The openlog() call that sets the syslog facility is in
      <strong>src/osdep/unix/env_unix.c</strong> in routine
      <strong>server_init()</strong>. You need to edit this file to change
      the syslog facility from LOG_MAIL to the facility you want, then
      rebuild. You also need to set up your /etc/syslog.conf properly.

      <p>Refer to the man pages for syslog and syslogd for more information
      on what the available syslog facilities are and how to configure
      syslogs. If you still don't understand what to do, find a UNIX system
      expert.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="security">5. Security Questions</a></h2>
  <hr>

  <p><a name="5.1"><strong>5.1 I see that the IMAP server allows access to
     arbitary files on the system, including /etc/passwd! How do I disable
     this?</strong></a></p>

  <dl>
    <dd>
      You should not worry about this if your IMAP users are allowed shell
      access. The IMAP server does not permit any access that the user can
      not have via the shell.

      <p>If, and only if, you deny your IMAP users shell access, you may want
      to consider one of three choices. Note that these choices reduce IMAP
      functionality, and may have undesirable side effects. Each of these
      choices involves an edit to file
      <strong>src/osdep/unix/env_unix.c</strong></p>

      <p>The first (and recommended) choice is to set
      <strong>restrictBox</strong> as described in file CONFIG. This will
      disable access to the filesystem root, to other users' home directory,
      and to superior directory.</p>

      <p>The second (and strongly NOT recommended) choice is to set
      <strong>closedBox</strong> as described in file CONFIG. This puts each
      IMAP session into a so-called "chroot jail", and thus setting this
      option is <em>extremely</em> dangerous; it can make your system much
      less secure and open to root compromise attacks. So do not use this
      option unless you are <em>absolutely certain</em> that you understand
      all the issues of a "chroot jail."</p>

      <p>The third choice is to rewrite routine
      <strong>mailboxfile()</strong> to implement whatever mapping from
      mailbox name to filesystem name (and restrictions) that you wish. This
      is the most general choice. As a guide, you can see at the start of
      routine <strong>mailboxfile()</strong> what the
      <strong>restrictBox</strong> choice does.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="5.2"><strong>5.2 I've heard that IMAP servers are insecure. Is this
     true?</strong></a></p>

  <dl>
    <dd>
      There are no known security problems in this version of the IMAP
      toolkit, including the IMAP and POP servers. The IMAP and POP servers
      limit what can be done while not logged in, and as part of the login
      process discard all privileges except those of the user.

      <p>As with other software packages, there have been buffer overflow
      vulnerabilities in past versions. All known problems of this nature are
      fixed in this version.</p>

      <p>There is every reason to believe that the bad guys are engaged in an
      ongoing effort to find vulnerabilities in the IMAP toolkit. We look for
      such problems, and when one is found we fix it.</p>

      <p>It's unfortunate that any vulnerabilities existed in past versions,
      and we're doing my best to keep the IMAP toolkit free of
      vulnerabilities. No new vulnerabilities have been discovered in quite a
      while, but efforts will not be relaxed.</p>

      <p>Beware of vendors who claim that their implementations can not have
      vulnerabilities.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="5.3"><strong>5.3 How do I know that I have the most secure version
     of the server?</strong></a></p>

  <dl>
    <dd>
      The best way is to keep your server software up to date. The bad guys
      are always looking for ways to crack software, and when they find one,
      let all their friends know.

      <p>Oldtimers used to refer to a concept of <em>software rot</em>: if
      your software hasn't been updated in a while, it would "rot" -- tend to
      acquire problems that it didn't have when it was new.</p>

      <p>The latest release version of the IMAP toolkit is always available
      at <a href=
      "ftp://ftp.cac.washington.edu/mail/imap.tar.Z">ftp://ftp.cac.washington.edu/mail/imap.tar.Z</a></p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="5.4"><strong>5.4 I see all these strcpy() and sprintf() calls, those
     are unsafe, aren't they?</strong></a></p>

  <dl>
    <dd>
      Yes and no.

      <p>It can be unsafe to do these calls if you do not know that the
      string being written will fit in the buffer. However, they are
      perfectly safe if you do know that.</p>

      <p>Beware of programmers who advocate doing a brute-force change of all
      instances of</p>
      <pre>
 strcpy (s,t);
</pre>to
      <pre>
 strncpy (s,t,n)[n] = '\0';
</pre>and similar measures in the name of "fixing all possible buffer
overflows."

      <p>There are examples in which a security bug was introduced because of
      this type of "fix", due to the programmer using the wrong value for n.
      In one case, the programmer thought that n was larger than it actually
      was, causing a NUL to be written out of the buffer; in another, n was
      too small, and a security credential was truncated.</p>

      <p>What is particularly ironic was that in both cases, the original
      strcpy() was safe, because the size of the source string was known to
      be safe.</p>

      <p>With all this in mind, the software has been inspected, and it is
      believed that all places where buffer overflows can happen have been
      fixed. The strcpy()s that are still are in the code occur after a size
      check was done in some other way.</p>

      <p>Note that the common C idiom of</p>
      <pre>
 *s++ = c;
</pre>is just as vulnerable to buffer overflows. You can't cure buffer
overflows by outlawing certain functions, nor is it desirable to do so;
sometimes operations like strcpy() translate into fast machine instructions
for better performance.

      <p>Nothing replaces careful study of code. That's how the bad guys find
      bugs. Security is not accomplished by means of brute-force
      shortcuts.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="5.5"><strong>5.5 Those /tmp lock files are protected 666, is that
     really right?</strong></a></p>

  <dl>
    <dd>
      Yes. Shared mailboxes won't work otherwise. Also, you get into
      accidental denial of service problems with old lock files left lying
      around; this happens fairly frequently.

      <p>The deliberate mischief that can be caused by fiddling with the lock
      files is small-scale; harassment level at most. There are many -- and
      much more effective -- other ways of harassing another user on UNIX.
      It's usually not difficult to determine the culprit.</p>

      <p>Before worrying about deliberate mischief, worry first about things
      happening by accident!</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="strange">6. <em>Why Did You Do This Strange Thing?</em>
     Questions</a></h2>
  <hr>

  <p><a name="6.1"><strong>6.1 Why don't you use GNU autoconfig / automake /
     autoblurdybloop?</strong></a></p>

  <dl>
    <dd>
      Autoconfig et al are not available on all the platforms where the IMAP
      toolkit is supported; and do not work correctly on some of the
      platforms where they do exist. Furthermore, these programs add another
      layer of complexity to an already complex process.

      <p>Coaxing software that uses autoconfig to build properly on platforms
      which were not specifically considered by that software wastes an
      inordinate amount of time. When (not if) autoconfig fails to do the
      right thing, the result is an inpenetrable morass to untangle in order
      to find the problem and fix it.</p>

      <p>The concept behind autoconfig is good, but the execution is flawed.
      It rarely does the right thing on a platform that wasn't specifically
      considered. Human life is too short to debug autoconfig problems,
      especially since the current mechanism is so much easier.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.2"><strong>6.2 Why do you insist upon a build with -g? Doesn't it
     waste disk and memory space?</strong></a></p>

  <dl>
    <dd>
      From time to time a submitted port has snuck in without -g. This has
      <em>always</em> ended up causing problems. There are only two valid
      excuses for not using -g in a port:

      <ul>
        <li>The compiler does not support -g</li>

        <li>An alternate form of -g is needed with optimization, e.g.
        -g3.</li>
      </ul>

      <p>There will be no new ports added without -g (or a suitable
      alternative) being set.</p>

      <p>-g has not been arbitrarily added to the ports which do not
      currently have it because we don't know if doing so would break the
      build. However, any support issues with one of those port <em>will</em>
      lead to the correct -g setting being determined and permanently
      added.</p>

      <p>Processors are fast enough (and disk space is cheap enough) that -g
      should be automatic in all compilers with no way of turning it off, and
      /bin/strip should be a symlink to /bin/true. Human life is too short to
      deal with binaries built without -g. Such binaries should be a bad
      memory of the days of KIPS processors and disks that costs several
      dollars per kilobyte.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.3"><strong>6.3 Why don't you make c-client a shared
     library?</strong></a></p>

  <dl>
    <dd>
      All too often, shared libraries create far more problems than they
      solve.

      <p>Remember that you only gain the benefit of a shared library when
      there are multiple applications which use that shared library. Even
      without shared libraries, on most modern operating systems (and many
      ancient ones too!) applications will share their text segments between
      across multiple processes running the same application. This means that
      if your system only runs one application (e.g. imapd) that uses the
      c-client library, then you gain no benefit from making c-client a
      shared library even if it has 100 imapd processes. You will, however
      suffer added complexity.</p>

      <p>If you have a server system that just runs imapd and ipop3d, then
      making c-client a shared library will save just one copy of c-client no
      matter how many IMAP/POP3 processes are running.</p>

      <p>The problem with shared libraries is that you have to keep around a
      copy of the library every time something changes in the library that
      would affect the interface the library presents to the application. So,
      you end up having many copies of the same shared library.</p>

      <p>If you don't keep multiple copies of the shared library, then one of
      two things happens. If there was proper versioning, then you'll get a
      message such as "cannot open shared object file" or "minor versions
      don't match" and the application won't run. Otherwise, the application
      will run, but will fail in mysterious ways.</p>

      <p>Several sites and third-party distributors have modified the
      c-client makefile in order to make c-client be a shared library.
      <em>When</em> (not <em>if</em>) a c-client based application fails in
      mysterious ways because of a library compatibility problem, the result
      is a bug report. A lot of time and effort ends up getting wasted
      investigating such bug reports.</p>

      <p>Memory is so cheap these days that it's not worth it. Human life is
      too short to deal with shared library compatibility problems.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.4"><strong>6.4 Why don't you use iconv() for internationalization
     support?</strong></a></p>

  <dl>
    <dd>iconv() is not ubiquitous enough.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.5"><strong>6.5 Why is the IMAP server connected to the home
     directory by default?</strong></a></p>

  <dl>
    <dd>
      The IMAP server has no way of knowing what you might call "mail" as
      opposed to "some other file"; in fact, you can use IMAP to access any
      file.

      <p>The IMAP server also doesn't know whether your preferred
      subdirectory for mailbox files is "mail/", ".mail/", "Mail/",
      "Mailboxes/", or any of a zillion other possibilities. If one such name
      were chosen, it would undoubtably anger the partisans of all the other
      names.</p>

      <p>It is possible to modify the software so that the default connected
      directory is someplace else. Please read the file CONFIG for discussion
      of this and other issues.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.6"><strong>6.6 I have a Windows system. Why isn't the server plug
     and play for me?</strong></a></p>

  <dl>
    <dd>
      There is no standard for how mail is stored on Windows; nor a single
      standard SMTP server. The closest to either would be the SMTP server in
      Microsoft's IIS.

      <p>So there's no default by which to make assumptions. As the software
      is set up, it assumes that the each user has an Windows login account
      and private home directory, and that mail is stored on that home
      directory as files in one of the popular UNIX formats. It also assumes
      that there is some tool equivalent to inetd on UNIX that does the
      TCP/IP listening and server startup.</p>

      <p>Basically, unless you're an email software hacker, you probably want
      to look elsewhere if you want IMAP/POP servers for Windows.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.7"><strong>6.7 I looked at the UNIX SSL code and saw that you have
     the SSL data payload size set to 8192 bytes. SSL allows 16K; why aren't
     you using the full size?</strong></a></p>

  <dl>
    <dd>
      This is to avoid an interoperability problem with:

      <ul>
        <li>PC IMAP clients that use Microsoft's SChannel.DLL (SSPI) for SSL
        support</li>

        <li>Microsoft Exchange server (which also uses SChannel).</li>
      </ul>

      <p>SChannel has a bug that makes it think that the maximum SSL data
      payload size is 16379 bytes -- 5 bytes too small. Thus, c-client has to
      make sure that it never transmits full sized SSL packets.</p>

      <p>The reason for using 8K (as opposed to, say, 16379 bytes, or 15K,
      or...) is that it corresponds with the TCP buffer size that the
      software uses elsewhere for input; there's a slight performance benefit
      to having the two sizes correspond or at least be a multiple of each
      other. Also, it keeps the size as a power of two, which might be
      significant on some platforms.</p>

      <p>There wasn't a significant difference that we could measure between
      8K and 15K.</p>

      <p>Microsoft has developed a hotfix for this bug. Look up MSKB article
      number 300562. Contrary to the article text which implies that this is
      a Pine issue, this bug also affects Microsoft Exchange server with
      <em>any</em> client that transmits full-sized SSL payloads.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.8"><strong>6.8 Why is an mh format INBOX called #mhinbox instead
     of just INBOX?</strong></a></p>

  <dl>
    <dd>
      It's a long story. In brief, the mh format driver is less functional
      than any of the other drivers. It turned out that there were some users
      (including high-level administrators) who tried mh years ago and no
      longer use it, but still had an mh profile left behind.

      <p>When the mh driver used INBOX, it would see the mh profile, and
      proceed to move the user's INBOX into the mh format INBOX. This caused
      considerable confusion as some things stopped working.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.9"><strong>6.9 Why don't you support the maildir
     format?</strong></a></p>

  <dl>
    <dd>
      It is technically difficult to support maildir in IMAP while
      maintaining acceptable performance, robustness, following the
      requirements of the IMAP protocol specification, and following the
      requirements of maildir.

      <p>No one has succeeded in accomplishing all four together. The various
      maildir drivers offered as patches all have these problems. The problem
      is exacerbated because this implementation supports multiple formats;
      consequently this implementation can't make any performance shortcuts
      by assuming that all the world is maildir.</p>

      <p>We can't do a better job than the maildir fan community has done
      with their maildir drivers. Similarly, if the maildir fan community
      provides the maildir driver, they take on the responsibility for
      answering maildir-specific support questions. This is as it should be,
      and that is why maildir support is left to the maildir fan
      community.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.10"><strong>6.10 Why don't you support the Cyrus
     format?</strong></a></p>

  <dl>
    <dd>
      There's no point to doing so. An implementation which supports multiple
      formats will never do as well as one which is optimized to support one
      single format.

      <p>If you want to use Cyrus mailbox format, you should use the Cyrus
      server, which is the native implementation of that format and is
      specifically optimized for that format. That's also why Cyrus doesn't
      implement any other format.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.11"><strong>6.11 Why is it creating extra forks on my SVR4
     system?</strong></a></p>

  <dl>
    <dd>
      This is because your system only has fcntl() style locking and not
      flock() style locking. fcntl() locking has a design flaw that causes a
      close() to release any locks made by that process on the file opened on
      that file descriptor, even if the lock was made on a different file
      descriptor.

      <p>This design flaw causes unexpected loss of lock, and consequent
      mailbox corruption. The workaround is to do certain "dangerous
      operations" in another fork, thus avoiding doing a close() in the
      vulnerable fork.</p>

      <p>The best way to solve this problem is to upgrade your SVR4 (Solaris,
      AIX, HP-UX, SGI) or OSF/1 system to a more advanced operating system,
      such as Linux or BSD. These more advanced operating systems have
      fcntl() locking for compatibility with SVR4, but also have flock()
      locking.</p>

      <p>Beware of certain SVR4 systems, such as AIX, which have an "flock()"
      function in their C library that is just a jacket that does an fcntl()
      lock. This is not a true flock(), and has the same design flaw as
      fcntl().</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.12"><strong>6.12 Why are you so fussy about the date/time format in
     the internal <code>"From&nbsp;"</code> line in traditional UNIX mailbox
     files? My other mail program just considers every line that starts with
     <code>"From&nbsp;"</code> to be the start of the message.</strong></a></p>

  <dl>
    <dd>
      You just answered your own question. If any line that starts with
      <code>"From&nbsp;"</code> is treated as the start of a message, then
      every message text line which starts with <code>"From&nbsp;"</code> has
      to be quoted (typically by prefixing a "&gt;" character). People
      complain about this -- "why did a &gt; get stuck in my message?"

      <p>So, good mail reading software only considers a line to be a
      <code>"From&nbsp;"</code> line if it follows the actual specification
      for a "From&nbsp;" line. This means, among other things, that the day of
      week is fixed-format: <code>"May&nbsp;14"</code>, but
      <code>"May&nbsp;&nbsp;7"</code> (note the extra space) as opposed to
      <code>"May&nbsp;7"</code>. ctime() format for the date is the most
      common, although POSIX also allows a numeric timezone after the
      year. For compatibility with ancient software, the seconds are optional,
      the timezone may appear before the year, the old 3-letter timezones are
      also permitted, and "remote from xxx" may appear after the whole
      thing.</p>

      <p>Unfortunately, some software written by novices use other formats.
      The most common error is to have a variable-width day of month, perhaps
      in the erroneous belief that RFC 2822 (or RFC 822) defines the format of
      the date/time in the <code>"From&nbsp;"</code> line (it doesn't; no RFC
      describes internal formats). I've seen a few other goofs, such as a
      single-digit second, but these are less common.</p>

      <p>If you are writing your own software that writes mailbox files, and
      you really aren't all that savvy with all the ins and outs and ancient
      history, you should seriously consider using the c-client library (e.g.
      routine mail_append()) instead of doing the file writes yourself. If
      you must do it yourself, use ctime(), as in:</p>
      <pre>
 fprintf (mbx,"From %s@%h %s",user,host,ctime (time (0)));
</pre>rather than try to figure out a good format yourself. ctime() is the
most traditional format and nobody will flame you for using it.
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.13"><strong>6.13 Why is traditional UNIX format the default
     format?</strong></a></p>

  <dl>
    <dd>Compatibility with the past 30 or so years of UNIX history. This
    server is the only one that completely interoperates with legacy UNIX
    mail tools.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.14"><strong>6.14 Why do you write this "DON'T DELETE THIS MESSAGE
     -- FOLDER INTERNAL DATA" message at the start of traditional UNIX and
     MMDF format mailboxes?</strong></a></p>

  <dl>
    <dd>
      This pseudo-message serves two purposes.

      <p>First, it establishes the mailbox format even when the mailbox has
      no messages. Otherwise, a mailbox with no messages is a zero-byte file,
      which could be one of several formats.</p>

      <p>Second, it holds mailbox metadata used by IMAP: the UID validity,
      the last assigned UID, and mailbox keywords. Without this metadata,
      which must be preserved even when the mailbox has no messages, the
      traditional UNIX format wouldn't be able to support the full
      capabilities of IMAP.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.15"><strong>6.15 Why don't you stash the mailbox metadata in the
     first real message of the mailbox instead of writing this fake FOLDER
     INTERNAL DATA message?</strong></a></p>

  <dl>
    <dd>
      In fact, that is what is done if the mailbox is non-empty and does not
      already have a FOLDER INTERNAL DATA message.

      <p>One problem with doing that is that if some external program removes
      the first message, the metadata is lost and must be recreated, thus
      losing any prior UID or keyword list status that IMAP clients may
      depend upon.</p>

      <p>Another problem is that this doesn't help if the last message is
      deleted. This will result in an empty mailbox, and the necessity to
      create a FOLDER INTERNAL DATA message.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.16"><strong>6.16 Why aren't "dual-use" mailboxes the
     default?</strong></a></p>

  <dl>
    <dd>Compatibility with the past 30 or so years of UNIX history, not to
    mention compatibility with user expectations when using shell tools.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.17"><strong>6.17 Why do you use ucbcc to build on
     Solaris?</strong></a></p>

  <dl>
    <dd>
      It is a long, long story about why cc is set to ucbcc. You need to
      invoke the C compiler so that it links with the SVR4 libraries and not
      the BSD libraries, otherwise readdir() will return the wrong
      information.

      <p>Of all the names in the most common path, ucbcc is the only name to
      be found (on /usr/ccs/bin) that points to a suitable compiler. cc is
      likely to be /usr/ucb/cc which is absolutely not the compiler that you
      want. The real SVR4 cc is probably something like /opt/SUNWspro/bin/cc
      which is rarely in anyone's path by default.</p>

      <p>ucbcc is probably a link to acc, e.g. /opt/SUNWspro/SC4.0/bin/acc,
      and is the UCB C compiler using the SVR4 libraries.</p>

      <p>If ucbcc isn't on your system, then punt on the SUN C compiler and
      use gcc instead (the gso port instead of the sol port).</p>

      <p>If, in spite of all the above warnings, you choose to change "ucbcc"
      to "cc", you will probably find that the -O2 needs to be changed to -O.
      If you don't get any error messages with -O2, that's a pretty good
      indicator that you goofed and are running the compiler that will link
      with the BSD libraries.</p>

      <p>To recap:</p>

      <ul>
        <li>The sol port is designed to be built using the UCB compiler using
        the SVR4 libraries. This compiler is "ucbcc", which is lunk to acc.
        You use -O2 as one of the CFLAGS.</li>

        <li>If you build the sol port with the UCB compiler using the BSD
        libraries, you will get no error messages but you will get bad
        binaries (the most obvious symptom is dropping the first two
        characters return filenames from the imapd LIST command. This
        compiler also uses -O2, and is very often what the user gets from
        "cc". <strong>BEWARE</strong></li>

        <li>If you build the sol port with the real SVR4 compiler, which is
        often hidden away or unavailable on many systems, then you will get
        errors from -O2 and you need to change that to -O. But you will get a
        good binary. However, you should try it with -O2 first, to make sure
        that you got this compiler and not the UCB compiler using BSD
        libraries.</li>
      </ul>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.18"><strong>6.18 Why should I care about some old system with BSD
     libraries? cc is the right thing on my Solaris system!</strong></a></p>

  <dl>
    <dd>
      Because there still are sites that use such systems. On those systems,
      the assumption that "cc" does the right thing will lead to corrupt
      binaries with no error message or other warning that anything is amiss.

      <p>Too many sites have fallen victim to this problem.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.19"><strong>6.19 Why do you insist upon writing .lock files in the
     spool directory?</strong></a></p>

  <dl>
    <dd>Compatibility with the past 30 years of UNIX software which deals
    with the spool directory, especially software which delivers mail.
    Otherwise, it is possible to lose mail.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="6.20"><strong>6.20 Why should I care about compatibility with the
     past?</strong></a></p>

  <dl>
    <dd>This is one of those questions in which the answer never convinces
    those who ask it. Somehow, everybody who ever asks this question ends up
    answering it for themselves as they get older, with the very answer that
    they rejected years earlier.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="problems">7. Problems and Annoyances</a></h2>
  <hr>

  <p><a name="7.1"><strong>7.1 Help! My INBOX is empty! What happened to my
     messages?</strong></a></p>

  <dl>
    <dd>
      If you are seeing "0 messages" when you open INBOX and you know you
      have messages there (and perhaps have looked at your mail spool file
      and see that messages are there), then probably there is something
      wrong with the very first line of your mail spool file. Make sure that
      the first five bytes of the file are "From ", followed by an email
      address and a date/time in ctime() format, e.g.:
      <pre>
 From fred@foo.bar Mon May  7 20:54:30 2001
</pre>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.2"><strong>7.2 Help! All my messages in a non-INBOX mailbox have
     been concatenated into one message which claims to be from me and has a
     subject of the file name of the mailbox! What's going
     on?</strong></a></p>

  <dl>
    <dd>
      Something wrong with the very first line of the mailbox. Make sure that
      the first five bytes of the file are "From ", followed by an email
      address and a date/time in ctime() format, e.g.:
      <pre>
 From fred@foo.bar Mon May  7 20:54:30 2001
</pre>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.3"><strong>7.3 Why do I get the message:</strong> <tt>CREATE
     failed: Can't create mailbox node xxxxxxxxx: File exists</tt>
     <strong>and how do I fix it?</strong></a></p>

  <dl>
    <dd>See the answer to the <a href="#1.8">Are hierarchical mailboxes
    supported?</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.4"><strong>7.4 Why can't I log in to the server? The user name and
     password are right!</strong></a></p>

  <dl>
    <dd>
      There are a myriad number of possible answers to this question. The
      only way to say for sure what is wrong is run the server under a
      debugger such as gdb while root (yes, you must be root) with a
      breakpoint at routines checkpw() and loginpw(), then single-step until
      you see which test rejected you. The server isn't going to give any
      error messages other than "login failed" in the name of not giving out
      any unnecessary information to unauthorized individuals.

      <p>Here are some of the more common reasons why login may fail:</p>

      <ul>
        <li>You didn't really give the correct user name and/or
        password.</li>

        <li>Your client doesn't send the LOGIN command correctly; for
        example, IMAP2 clients won't send a password containing a "*"
        correctly to an IMAP4 server.</li>

        <li>If you have set up a CRAM-MD5 database, remember that the
        password used is the one in the CRAM-MD5 database, and furthermore
        that there must also be an entry in /etc/passwd (but the /etc/passwd
        password is not used).</li>

        <li>If you are using PAM, have you created a service file for the
        server in /etc/pam.d?</li>

        <li>If you are using shadow passwords, have you used an appropriate
        port when building? In particular, note that "lnx" is for Linux
        systems without shadow passwords; you probably want "slx" or "lnp"
        instead.</li>

        <li>If your system has account or password expirations, check to see
        that the expiration date hasn't passed.</li>

        <li>You can't log in as root or any other UID 0 user. This is for
        your own safety, not to mention the fact that the servers use UID 0
        as meaning "not logged in".</li>
      </ul>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.5"><strong>7.5 Help! My load average is soaring and I see hundreds
     of POP and IMAP servers, many logged in as the same
     user!</strong></a></p>

  <dl>
    <dd>
      Certain inferior losing GUI mail reading programs have a "synchronize
      all mailboxes at startup" (IMAP) or "check for new mail every second"
      (POP) feature which causes a rapid and unchecked spawning of servers.

      <p>This is not a problem in the server; the client is really asking for
      all those server sessions. Unfortunately, there isn't much that the POP
      and IMAP servers can do about it; they don't spawned themselves.</p>

      <p>Some sites have added code to record the number of server sessions
      spawned per user per hour, and disable login for a user who has
      exceeded a predetermined rate. This doesn't stop the servers from being
      spawned; it just means that a server session will commit suicide a bit
      faster.</p>

      <p>Another possibility is to detect excessive server spawning activity
      at the level where the server is spawned, which would be inetd or
      possibly tcpd. The problem here is that this is a hard time to
      quantify. 50 sessions in a minute from a multi-user timesharing system
      may be perfectly alright, whereas 10 sessions a minute from a PC may be
      too much.</p>

      <p>The real solution is to fix the client configuration, by disabling
      those evil features. Also tell the vendors of those clients how you
      feel about distributing denial-of-service attack tools in the guise of
      mail reading programs.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.6"><strong>7.6 Why does mail disappear even though I set "keep
     mail on server"?</strong></a><br>
  <a name="7.7"><strong>7.7 Why do I get the message</strong> <tt>Moved #####
     bytes of new mail to /home/user/mbox from /var/spool/mail/user</tt>
     <strong>and why did this happen?</strong></a></p>

  <dl>
    <dd>
      This is probably caused by the mbox driver. If the file "mbox" exists
      on the user's home directory and is in UNIX mailbox format, then when
      INBOX is opened this file will be selected as INBOX instead of the mail
      spool file. Messages will be automatically transferred from the mail
      spool file into the mbox file.

      <p>To disable this behavior, delete "mbox" from the EXTRADRIVERS list
      in the top-level Makefile and rebuild. Note that if you do this, users
      won't be able to access the messages that have already been moved to
      mbox unless they open mbox instead of INBOX.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.8"><strong>7.8 Why isn't it showing the local host name as a
     fully-qualified domain name?</strong></a><br>
  <a name="7.9"><strong>7.9 Why is the local host name in the
     From/Sender/Message-ID headers of outgoing mail not coming out as a
     fully-qualified domain name?</strong></a></p>

  <dl>
    <dd>
      Your UNIX system is misconfigured. The entry for your system in
      /etc/hosts must have the fully-qualified domain name first, e.g.
      <pre>
 105.69.1.234	myserver.example.com myserver
</pre>

      <p>A common mistake of novice system administrators is to have the
      short name first, e.g.</p>
      <pre>
 105.69.1.234	myserver myserver.example.com

</pre>

      <p>or to omit the fully qualified domain name entirely, e.g.</p>
      <pre>
 105.69.1.234	myserver
</pre>

      <p>The result of this is that when the IMAP toolkit does a
      gethostbyname() call to get the fully-qualified domain name, it would
      get "myserver" instead of "myserver.example.com".</p>

      <p>On some systems, a configuration file (typically named
      /etc/svc.conf, /etc/netsvc.conf, or /etc/nsswitch.conf) can be used to
      configure the system to use the domain name system (DNS) instead of
      /etc/hosts, so it doesn't matter if /etc/hosts is misconfigured.</p>

      <p>Check the man pages for gethostbyname, hosts, svc, and/or netsvc for
      more information.</p>

      <p>Unfortunately, certain vendors, most notably SUN, have failed to
      make this clear in their documentation. Most of SUN's documentation
      assumes a corporate network that is not connected to the Internet.</p>

      <p>net.folklore once (late 1980s) held that the proper procedure was to
      append the results of getdomainname() to the name returned by
      gethostname(), and some versions of sendmail configuration files were
      distributed that did this. This was incorrect; the string returned from
      getdomainname() is the Yellow Pages (a.k.a NIS) domain name, which is a
      completely different (albeit unfortunately named) entity from an
      Internet domain. These were often fortuitously the same string, except
      when they weren't. Frequently, this would result in host names with
      spuriously doubled domain names, e.g.</p>
      <pre>
 myserver.example.com.example.com

</pre>

      <p>This practice has been thoroughly discredited for many years, but
      folklore dies hard.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.10"><strong>7.10 What does the message:</strong> <tt>Mailbox
     vulnerable - directory /var/spool/mail must have 1777 protection</tt>
     <strong>mean? How can I fix this?</strong></a></p>

  <dl>
    <dd>
      In order to update a mailbox in the default UNIX format, it is
      necessary to create a lock file to prevent the mailer from delivering
      mail while an update is in progress. Some systems use a directory
      protection of 775, requiring that all mail handling programs be setgid
      mail; or of 755, requiring that all mail handling programs be setuid
      root.

      <p>The IMAP toolkit does not run with any special privileges, and I
      plan to keep it that way. It is antithetical to the concept of a
      toolkit if users can't write their own programs to use it. Also, I've
      had enough bad experiences with security bugs while running privileged;
      the IMAP and POP servers have to be root when not logged in, in order
      to be able to log themselves in. I don't want to go any deeper down
      that slippery slope.</p>

      <p>Directory protection 1777 is secure enough on most well-managed
      systems. If you can't trust your users with a 1777 mail spool (petty
      harassment is about the limit of the abuse exposure), then you have
      much worse problems then that.</p>

      <p>If you absolutely insist upon requiring privileges to create a lock
      file, external file locking can be done via a setgid mail program named
      /etc/mlock (this is defined by LOCKPGM in the c-client Makefile). If
      the toolkit is unable to create a &lt;...mailbox...&gt;.lock file in
      the directory by itself, it will try to call mlock to do it. I do not
      recommend doing this for performance reasons.</p>

      <p>A sample mlock program is included as part of imap-2007. We have
      tried to make this sample program secure, but it has not been
      thoroughly audited.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.11"><strong>7.11 What does the message:</strong> <tt>Mailbox is
     open by another process, access is readonly</tt> <strong>mean? How do I
     fix this?</strong></a></p>

  <dl>
    <dd>
      A problem occurred in applying a lock to a /tmp lock file. Either some
      other program has the mailbox open and won't relenquish it, or
      something is wrong with the protection of /tmp or the lock.

      <p>Make sure that the /tmp directory is protected 1777. Some security
      scripts incorrectly set the protection of the /tmp directory to 775,
      which disables /tmp for all non-privileged programs.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.12"><strong>7.12 What does the message:</strong> <tt>Can't get
     write access to mailbox, access is readonly</tt>
     <strong>mean?</strong></a></p>

  <dl>
    <dd>The mailbox file is write-protected against you.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.13"><strong>7.13 I set my POP3 client to "delete messages from
     server" but they never get deleted. What is wrong?</strong></a></p>

  <dl>
    <dd>
      Make sure that your mailbox is not read-only: that the mailbox is owned
      by you and write enabled (protection 0600), and that the /tmp directory
      is longer world-writeable. /tmp must be world-writeable because lots of
      applications use it for scratch space. To fix this, do
      <pre>

 chmod 1777 /tmp
</pre>as root.

      <p>Make sure that your POP3 client issues a QUIT command when it
      finishes. The POP3 protocol specifies that deletions are discarded
      unless a proper QUIT is done.</p>

      <p>Make sure that you are not opening multiple POP3 sessions to the
      same mailbox. It is a requirement of the POP3 protocol than only one
      POP3 session be in effect to a mailbox at a time, however some,
      poorly-written POP3 clients violate this. Also, some background "check
      for new mail" tasks also cause a violation. See the answer to the
      <a href="#7.19">What does the syslog message: Killed (lost mailbox
      lock) user=... host=... mean?</a> question for more details.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.14"><strong>7.14 What do messages such as:</strong></a></p>
  <pre>
 Message ... UID ... already has UID ...
 Message ... UID ... less than ...
 Message ... UID ... greater than last ...
 Invalid UID ... in message ..., rebuilding UIDs
</pre>

  <p><strong>mean?</strong></p>

  <dl>
    <dd>
      Something happened to corrupt the unique identifier regime in the
      mailbox. In traditional UNIX-format mailboxes, this can happen if the
      user deleted the "DO NOT DELETE" internal message.

      <p>This problem is relatively harmless; a new valid unique identifier
      regime will be created. The main effect is that any references to the
      old UIDs will no longer be useful.</p>

      <p>So, unless it is a chronic problem or you feel like debugging, you
      can safely ignore these messages.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.15"><strong>7.15 What do the error messages:</strong></a></p>
  <pre>
 Unable to read internal header at ...
 Unable to find CRLF at ...
 Unable to parse internal header at ...
 Unable to parse message date at ...
 Unable to parse message flags at ...
 Unable to parse message UID at ...
 Unable to parse message size at ...
 Last message (at ... ) runs past end of file ...
</pre>

  <p><strong>mean? I am using mbx format.</strong></p>

  <dl>
    <dd>
      The mbx-format mailbox is corrupted and needs to be repaired.

      <p>You should make an effort to find out why the corruption happened.
      Was there an obvious system problem (crash or disk failure)? Did the
      user accidentally access the file via NFS? Mailboxes don't get
      corrupted by themselves; something caused the problem.</p>

      <p>Some people have developed automated scripts, but if you're
      comfortable using emacs it's pretty easy to fix it manually. Do
      <em>not</em> use vi or any other editor unless you are certain that
      editor can handle binary!!!</p>

      <p>If you are not comfortable with emacs, or if the file is too large
      to read with emacs, see the "step-by-step" technique later on for
      another way of doing it.</p>

      <p>After the word "at" in the error message is the byte position it got
      to when it got unhappy with the file, e.g. if you see:</p>
      <pre>
 Unable to parse internal header at 43921: ne bombastic blurdybloop
</pre>The problem occurs at the 43,931 byte in the file. That's the point you
need to fix. c-client is expecting an internal header at that byte number,
looking something like:
      <pre>
 6-Jan-1998 17:42:24 -0800,1045;000000100001-00000001
</pre>The format of this internal line is:
      <pre>
 dd-mmm-yyyy hh:mm:ss +zzzz,ssss;ffffffffFFFF-UUUUUUUU
</pre>The only thing that is variable is the "ssss" field, it can be as many
digits as needed. All other fields (inluding the "dd") are fixed width. So,
the easiest thing to do is to look forward in the file for the next internal
header, and delete everything from the error point to that internal header.

      <p>Here's what to do if you want to be smarter and do a little bit more
      work. Generally, you're in the middle of a message, and there's nothing
      wrong with that message. The problem happened in the *previous*
      message. So, search back to the previous internal header. Now, remember
      that "ssss" field? That's the size of that message.</p>

      <p>Mark where you are in the file, move the cursor to the line after
      the internal header, and skip that many bytes ("ssss") forward. If
      you're at the point of the error in the file, then that message is
      corrupt. If you're at a different point, then perhaps the previous
      message is corrupt and has a too long size count that "ate" into this
      message.</p>

      <p>Basically, what you need to do is make sure that all those size
      counts are right, and that moving "ssss" bytes from the line after the
      internal header will land you at another internal header.</p>

      <p>Usually, once you know what you're looking at, it's pretty easy to
      work out the corruption, and the best remedial action. Repair scripts
      will make the problem go away but may not always do the smartest/best
      salvage of the user's data. Manual repair is more flexible and usually
      preferable.</p>

      <p>Here is a step-by-step technique for fixing corrupt mbx files that's
      a bit cruder than the procedure outlined above, but works for any size
      file.</p>

      <p>In this example, suppose that the corrupt file is INBOX, the error
      message is</p>
      <pre>
 Unable to find CRLF at 132551754
</pre>and the size of the INBOX file is 132867870 bytes.

      <p>The first step is to split the mailbox file at the point of the
      error:</p>

      <ul>
        <li>Rename the INBOX file to some other name, such as INBOX.bad.</li>

        <li>Copy the first 132,551,754 bytes of INBOX.bad to another file,
        such as INBOX.new.</li>

        <li>Extract the trailing 316,116 bytes (132867870-132551754) of
        INBOX.bad into another file, such as INBOX.tail.</li>

        <li>You no longer need INBOX.bad. Delete it.</li>
      </ul>In other words, use the number from the "Unable to find CRLF at"
      as the point to split INBOX into two new files, INBOX.new and
      INBOX.tail.

      <p>Now, remove the erroneous data:</p>

      <ul>
        <li>Verify that you can open INBOX.new in IMAP or Pine.</li>

        <li>The last message of INBOX.new is probably corrupted. Copy it to
        another file, such as badmsg.1, then delete and expunge that last
        message from INBOX.new</li>

        <li>Locate the first occurance of text in INBOX.tail which looks like
        an internal header, as described above.</li>

        <li>Remove all the text which occurs prior to that point, and place
        it into another file, such as badmsg.2. Note that in the case of a
        single digit date, there is a leading space which must not be removed
        (e.g. " 6-Nov-2001" not "6-Nov-2001").</li>
      </ul>

      <p>Reassemble the mailbox:</p>

      <ul>
        <li>Append INBOX.tail to INBOX.new.</li>

        <li>You no longer need INBOX.tail. Delete it.</li>

        <li>Verify that you can open INBOX.new in IMAP or Pine.</li>
      </ul>

      <p>Reinstall INBOX.new as INBOX:</p>

      <ul>
        <li>Check to see if you have received any new messages while
        repairing INBOX.</li>

        <li>If you haven't received any new messages while repairing INBOX,
        just rename INBOX.new to INBOX.</li>

        <li>If you have received new messages, be sure to copy the new
        messages from INBOX to INBOX.new before doing the rename.</li>
      </ul>

      <p>You now have a working INBOX, as well as two files with corrupted
      data (badmsg.1 and badmsg.2). There may be some useful data in the two
      badmsg files that you might want to try salvaging; otherwise you can
      delete the two badmsg files.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.16"><strong>7.16 What do the syslog messages:</strong></a></p>
  <pre>

 imap/tcp server failing (looping)
 pop3/tcp server failing (looping)
</pre>

  <p><strong>mean? When it happens, the listed service shuts down. How can I
  fix this?</strong></p>

  <dl>
    <dd>
      The error message "server failing (looping), service terminated" is not
      from either the IMAP or POP servers. Instead, it comes from inetd, the
      daemon which listens for TCP connections to a number of servers,
      including the IMAP and POP servers.

      <p>inetd has a limit of 40 new server sessions per minute for any
      particular service. If more than 40 sessions are initiated in a minute,
      inetd will issue the "failing (looping), service terminated" message
      and shut down the service for 10 minutes. inetd does this to prevent
      system resource consumption by a client which is spawning infinite
      numbers of servers. It should be noted that this is a denial of
      service; however for some systems the alternative is a crash which
      would be a worse denial of service!</p>

      <p>For larger server systems, the limit of 40 is much too low. The
      limit was established many years ago when a system typically only ran a
      few dozen servers.</p>

      <p>On some versions of inetd, such as the one distributed with most
      versions of Linux, you can modify the <strong>/etc/inetd.conf</strong>
      file to have a larger number of servers by appending a period followed
      by a number after the <strong>nowait</strong> word for the server
      entry. For example, if your existing /etc/inetd.conf line reads:</p>
      <pre>
 imap    stream  tcp     nowait  root    /usr/etc/imapd imapd
</pre>try changing it to be:
      <pre>
 imap    stream  tcp     nowait.100  root    /usr/etc/imapd imapd
</pre>Another example (using TCP wrappers):
      <pre>
 imap    stream  tcp     nowait  root    /usr/sbin/tcpd  imapd
</pre>try changing it to be:
      <pre>
 imap    stream  tcp     nowait.100  root    /usr/sbin/tcpd  imapd

</pre>to increase the limit to 100 sessions/minute.

      <p>Before making this change, please read the information in "man
      inetd" to determine whether or not your inetd has this feature. If it
      does not, and you make this change, the likely outcome is that you will
      disable IMAP service entirely.</p>

      <p>Another way to fix this problem is to edit the inetd.c source code
      (provided by your UNIX system vendor) to set higher limits, rebuild
      inetd, install the new binary, and reboot your system. This should only
      be done by a UNIX system expert. In the inetd.c source code, the limits
      <strong>TOOMANY</strong> (normally 40) is the maximum number of new
      server sessions permitted per minute, and <strong>RETRYTIME</strong>
      (normally 600) is the number of seconds inetd will shut down the server
      after it exceeds TOOMANY.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.17"><strong>7.17 What does the syslog message:</strong>
     <tt>Mailbox lock file /tmp/.600.1df3 open failure: Permission
     denied</tt> <strong>mean?</strong></a></p>

  <dl>
    <dd>
      This usually means that some "helpful" security script person has
      protected /tmp so that it is no longer world-writeable. /tmp must be
      world-writeable because lots of applications use it for scratch space.
      To fix this, do
      <pre>
 chmod 1777 /tmp

</pre>as root.

      <p>If that isn't the answer, check the protection of the named file. If
      it is something other than 666, then either someone is hacking or some
      "helpful" person modified the code to have a different default lock
      file protection.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.18"><strong>7.18 What do the syslog messages:</strong></a></p>
  <pre>
 Command stream end of file, while reading line user=... host=...
 Command stream end of file, while reading char user=... host=...
 Command stream end of file, while writing text user=... host=...
</pre>

  <p><strong>mean?</strong></p>

  <dl>
    <dd>
      This message occurs when the session is disconnected without a proper
      LOGOUT (IMAP) or QUIT (POP) command being received by the server first.

      <p>In many cases, this is perfectly normal; many client implementations
      are impolite and do this. Some programmers think this sort of rudeness
      is "more efficient".</p>

      <p>The condition could, however, indicate a client or network
      connectivity problem. The server has no way of knowing whether there's
      a problem or just a rude client, so it issues this message instead of a
      Logout.</p>

      <p>Certain inferior losing clients disconnect abruptly after a failed
      login, and instead of saying that the login failed, just say that they
      can't access the mailbox. They then complain to the system manager, who
      looks in the syslog and finds this message. Not very helpful, eh? See
      the answer to the <a href="#7.4">Why can't I log in to the server? The
      user name and password are right!</a> question.</p>

      <p>If the user isn't reporting a problem, you can probably ignore this
      message.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.19"><strong>7.19 Why did my POP or IMAP session suddenly
     disconnect? The syslog has the message:</strong> <tt>Killed (lost
     mailbox lock) user=... host=...</tt></a></p>

  <dl>
    <dd>
      This message only happens when either the traditional UNIX mailbox
      format or MMDF format is in use. This format only allows one session to
      have the mailbox open read/write at a time.

      <p>The servers assume that if a second session attempts to open the
      mailbox, that means that the first session is probably owned by an
      abandoned client. The common scenario here is a user who leaves his
      client running at the office, and then tries to read his mail from
      home. Through an internal mechanism called <em>kiss of death</em>, the
      second session requests the first session to kill itself. When the
      first session receives the "kiss of death", it issues the "Killed (lost
      mailbox lock)" syslog message and terminates. The second session then
      seizes read/write access, and becomes the new "first" session.</p>

      <p>Certain poorly-designed clients routinely open multiple sessions to
      the same mailbox; the users of those clients tend to get this message a
      lot.</p>

      <p>Another cause of this message is a background "check for new mail"
      task which does its work by opening a POP session to server every few
      seconds. They do this because POP doesn't have a way to announce new
      mail.</p>

      <p>The solution to both situations is to replace the client with a good
      online IMAP client such as Pine. Life is too short to waste on POP
      clients and poorly-designed IMAP clients.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.20"><strong>7.20 Why does my IMAP client show all the files on the
     system, recursively from the UNIX root directory?</strong></a><br>
  <a name="7.21"><strong>7.21 Why does my IMAP client show all of my files,
     recursively from my UNIX home directory?</strong></a></p>

  <dl>
    <dd>
      A well-written client should only show one level of hierarchy and then
      stop, awaiting explicit user action before going lower. However, some
      poorly-designed clients will recursively list all files, which may be a
      very long list (especially if you have symbolic links to directories
      that create a loop in the filesystem graph!).

      <p>This behavior has also been observed in some third-party c-client
      drivers, including maildir drivers. Consequently, this problem has even
      been observed in Pine. It is important to understand that this is not a
      problem in Pine or c-client; it is a problem in the third-party driver.
      A Pine built without that third-party driver will not have this
      problem.</p>

      <p>See also the answer to <a href="#7.73">Why does my IMAP client show
      all my files in my home directory?</a></p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.22"><strong>7.22 Why does my IMAP client show that I have
     mailboxes named "#mhinbox", "#mh", "#shared", "#ftp", "#news", and
     "#public"?</strong></a></p>

  <dl>
    <dd>
      These are IMAP namespace names. They represent other hierarchies in
      which messages may exist. These hierarchies may not necessarily exist
      on a server, but the namespace name is still in the namespace list in
      order to mark it as reserved.

      <p>A few poorly-designed clients display all namespace names as if they
      were top-level mailboxes in a user's list of mailboxes, whether or not
      they actually exist. This is a flaw in those clients.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.23"><strong>7.23 Why does my IMAP client show all my files in my
     home directory?</strong></a></p>

  <dl>
    <dd>
      As distributed, the IMAP server is connected to your home directory by
      default. It has no way of knowing what you might call "mail" as opposed
      to "some other file"; in fact, you can use IMAP to access any file.

      <p>Most clients have an option to configure your connected directory on
      the IMAP server. For example, in Pine you can specify this as the
      "Path" in your folder-collection, e.g.</p>
      <pre>
 Nickname  : Secondary Folders
 Server    : imap.example.com
 Path      : mail/
 View      : 
</pre>In this example, the user is connected to the "mail" subdirectory of
his home directory.

      <p>Other servers call this the "folder prefix" or similar term.</p>

      <p>It is possible to modify the IMAP server so that all users are
      automatically connected to some other directory, e.g. a subdirectory of
      the user's home directory. Read the file CONFIG for more details.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.24"><strong>7.24 Why is there a long delay before I get connected
     to the IMAP or POP server, no matter what client I use?</strong></a></p>

  <dl>
    <dd>
      There are two common occurances of this problem:

      <ul>
        <li>You are running a system (e.g. certain versions of Linux) which
        by default attempts to connect to an "IDENT" protocol (port 113)
        server on your client. However, a firewall or NAT box is blocking
        connections to that port, so the connection attempt times out.

          <p>The IDENT protocol is a well-known bad idea that does not
          deliver any real security but causes incredible problems. The idea
          is that this will give the server a record of the user name, or at
          least what some program listening on port 113 says is the user
          name. So, if somebody coming from port nnnnn on a system does
          something bad, IDENT may give you the userid of the bad guy.</p>

          <p>The problem is, IDENT is only meaningful on a timesharing system
          which has an administrator who is privileged and users who are not.
          It is of no value on a personal system which has no separate
          concept of "system administrator" vs. "unprivileged user".</p>

          <p>On either type of system, security-minded people either turn
          IDENT off or replace it with an IDENT server that lies. Among other
          things, IDENT gives spammers the ability to harvest email addresses
          from anyone who connects to a web page.</p>

          <p>This problem has been showing up quite frequently on systems
          which use xinetd instead of inetd. Look for files named
          /etc/xinetd.conf, /etc/xinetd.d/imapd, /etc/inetd.d/ipop2d, and
          /etc/xinetd.d/ipop3d. In those files, look for lines containing
          "USERID", e.g.</p>
          <pre>
 log_on_success += USERID
</pre>Hunt down such lines, and delete them ruthlessly from all files in
which they occur. Don't be shy about it.
        </li>

        <li>The DNS is taking a long time to do a reverse DNS (PTR record)
        lookup of the IP address of your client. This is a problem in your
        DNS, which either you or you ISP need to resolve. Ideally, the DNS
        should return the client's name; but if it can't it should at least
        return an error quickly.</li>
      </ul>

      <p>As you may have noticed, neither of these are actual problems in the
      IMAP or POP servers; they are configuration issues with either your
      system or your network infrastructure. If this is all new to you, run
      (don't walk) to the nearest technical bookstore and get yourself a good
      pedagogical text on system administration for the type of system you
      are running.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.25"><strong>7.25 Why is there a long delay in Pine or any other
     c-client based application call before I get connected to the IMAP
     server? The hang seems to be in the c-client mail_open() call. I don't
     have this problem with any other IMAP client. There is no delay
     connecting to a POP3 or NNTP server with mail_open().</strong></a></p>

  <dl>
    <dd>
      By default, the c-client library attempts to make a connection through
      rsh (and ssh, if you enable that). If the command:
      <pre>
 rsh imapserver exec /etc/rimapd

</pre>(or ssh if that is enabled) returns with a "* PREAUTH" response, it
will use the resulting rsh session as the IMAP session and not require an
authentication step on the server.

      <p>Unfortunately, rsh has a design error that treats "TCP connection
      refused" as "temporary failure, try again"; it expects the "rsh not
      allowed" case to be implemented as a successful connection followed by
      an error message and close the connection.</p>

      <p>It must be emphasized that this is a bug in rsh. It is <em>not</em>
      a bug in the IMAP toolkit.</p>

      <p>The use of rsh can be disabled in any the following ways:</p>

      <ul>
        <li>You can disable it for this particular session by either:

          <ul>
            <li>setting an explicit port number in the mailbox name, e.g.
              <pre>
 {imapserver.foo.com:143}INBOX
</pre>
            </li>

            <li>using SSL (the /ssl switch)</li>
          </ul>
        </li>

        <li>You can disable rsh globally by setting the rsh timeout value to
        0 with the call:
          <pre>
 mail_parameters (NIL,SET_RSHTIMEOUT,0);
</pre>
        </li>
      </ul>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.26"><strong>7.26 Why does a message sometimes get split into two
     or more messages on my SUN system?</strong></a></p>

  <dl>
    <dd>
      This is caused by an interaction of two independent design problems in
      SUN mail software. The first problem is that the "forward message"
      option in SUN's <em>mail tool</em> program includes the internal "From
      " header line in the text that it forwarded. This internal header line
      is specific to traditional UNIX mailbox files and is not suitable for
      use in forwarded messages.

      <p>The second problem is that the mail delivery agent assumes that mail
      reading programs will not use the traditional UNIX mailbox format but
      instead an incompatible variant that depends upon a
      <em>Content-Length:</em> message header. Content-Length is widely
      recognized to have been a terrible mistake, and is no longer
      recommended for use in mail (it is used in other facilities that use
      MIME).</p>

      <p>One symptom of the problem is that under certain circumstances, a
      message may get broken up into several messages. I'm also aware of
      security bugs caused by programs that foolishly trust "Content-Length:"
      headers with evil values.</p>

      <p>To fix the mailer on your system, edit your sendmail.cf to change
      the <strong>Mlocal</strong> line to have the <strong>-E</strong> flag.
      A typical entry will lool like:</p>
      <pre>
 Mlocal,	P=/usr/lib/mail.local, F=flsSDFMmnPE, S=10, R=20,
		A=mail.local -d $u
</pre>This fix will also work around the problem with mail tool, because it
will insert a "&gt;" before the internal header line to prevent it from being
interpreted by mail reading software as an internal header line.
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.27"><strong>7.27 Why did my POP or IMAP session suddenly
     disconnect? The syslog has the message:</strong></a></p>
  <pre>
 Autologout user=&lt;...my user name...&gt; host=&lt;...my client system...&gt;

</pre>

  <dl>
    <dd>
      This is a problem in your client.

      <p>In the case of IMAP, it failed to communicate with the IMAP server
      for over 30 minutes; in the case of POP, it failed to communicate with
      the POP server for over 10 minutes.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.28"><strong>7.28 What does the UNIX error message:</strong>
     <tt>TLS/SSL failure: myserver: SSL negotiation failed</tt>
     <strong>mean?</strong></a><br>
  <a name="7.29"><strong>7.29 What does the PC error message:</strong>
     <tt>TLS/SSL failure: myserver: Unexpected TCP input disconnect</tt>
     <strong>mean?</strong></a></p>

  <dl>
    <dd>
      This usually means that an attempt to negotiate TLS encryption via the
      STARTTLS command failed, because the server advertises STARTTLS
      functionality, but doesn't actually have it (e.g. because no
      certificates are installed).

      <p>Use the /notls option in the mailbox name to disable TLS
      negotiation.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.30"><strong>7.30 What does the error message:</strong> <tt>TLS/SSL
     failure: myserver: Server name does not match certificate</tt>
     <strong>mean?</strong></a></p>

  <dl>
    <dd>
      An SSL or TLS session encryption failed because the server name in the
      server's certificate does not match the name that you gave it. This
      could indicate that the server is not really the system you think that
      it is, but can be also be called if you gave a nickname for the server
      or name that was not fully-qualified. You must use the fully-qualified
      domain name for the server in order to validate its certificate

      <p>Use the /novalidate-cert option in the mailbox name to disable
      validation of the certificate.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.31"><strong>7.31 What does the UNIX error message:</strong>
     <tt>TLS/SSL failure: myserver: self-signed certificate</tt>
     <strong>mean?</strong></a><br>
  <a name="7.32"><strong>7.32 What does the PC error message:</strong>
     <tt>TLS/SSL failure: myserver: Self-signed certificate or untrusted
     authority</tt> <strong>mean?</strong></a></p>

  <dl>
    <dd>
      An SSL or TLS session encryption failed because your server's
      certificate is "self-signed"; that is, it is not signed by any
      Certificate Authority (CA) and thus can not be validated. A CA-signed
      certificate costs money, and some smaller sites either don't want to
      pay for it or haven't gotten one yet. The bad part about this is that
      this means there is no guarantee that the server is really the system
      you think that it is.

      <p>Use the /novalidate-cert option in the mailbox name to disable
      validation of the certificate.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.33"><strong>7.33 What does the UNIX error message:</strong>
     <tt>TLS/SSL failure: myserver: unable to get local issuer
     certificate</tt> <strong>mean?</strong></a></p>

  <dl>
    <dd>
      An SSL or TLS session encryption failed because your system does not
      have the Certificate Authority (CA) certificates installed on OpenSSL's
      certificates directory. On most systems, this directory is
      /usr/local/ssl/certs). As a result, it is not possible to validate the
      server's certificate.

      <p>If CA certificates are properly installed, you should see
      factory.pem and about a dozen other .pem names such as
      thawteCb.pem.</p>

      <p>As a workaround, you can use the /novalidate-cert option in the
      mailbox name to disable validation of the certificate; however, note
      that you are then vulnerable to various security attacks by bad
      guys.</p>

      <p>The correct fix is to copy all the files from the certs/ directory
      in the OpenSSL distribution to the /usr/local/ssl/certs (or whatever)
      directory. Note that you need to do this after building OpenSSL,
      because the OpenSSL build creates a number of needed symbolic links.
      For some bizarre reason, the OpenSSL "make install" doesn't do this for
      you, so you must do it manually.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.34"><strong>7.34 Why does reading certain messages hang when using
     Netscape? It works fine with Pine!</strong></a></p>

  <dl>
    <dd>
      There are two possible causes.

      <p>Check the mail syslog. If you see the message "Killed (lost mailbox
      lock)" for the impacted user(s), read the FAQ entry regarding that
      message.</p>

      <p>Check the affected mailbox to see if there are embedded NUL
      characters in the message. NULs in message texts are a technical
      violation of both the message format and IMAP specifications. Most
      clients don't care, but apparently Netscape does.</p>

      <p>You can work around this by rebuilding imapd with the
      <strong>NETSCAPE_BRAIN_DAMAGE</strong> option set (see
      src/imapd/Makefile); this will cause imapd to convert all NULs to 0x80
      characters. A better solution is to enable the feature in your MTA to
      MIME-convert messages with binary content. See the documentation for
      your MTA for how to do this.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.35"><strong>7.35 Why does Netscape say that there's a problem with
     the IMAP server and that I should "Contact your mail server
     administrator."?</strong></a></p>

  <dl>
    <dd>
      Certain versions of Netscape do this when you click the Manage Mail
      button, which uses an undocumented feature of Netscape's proprietary
      IMAP server.

      <p>You can work around this by rebuilding imapd with the
      <strong>NETSCAPE_BRAIN_DAMAGE</strong> option set (see
      src/imapd/Makefile) to a URL that points either to an alternative IMAP
      client (e.g. Pine) or perhaps to a homebrew mail account management
      page.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.36"><strong>7.36 Why is one user creating huge numbers of IMAP or
     POP server sessions?</strong></a></p>

  <dl>
    <dd>The user is probably using Outlook Express, Eudora, or a similar
    program. See the answer to the <a href="#7.5">Help! My load average is
    soaring and I see hundreds of POP and IMAP servers, many logged in as the
    same user!</a> question.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.37"><strong>7.37 Why don't I get any new mail notifications from
     Outlook Express or Outlook after a while?</strong></a></p>

  <dl>
    <dd>
      This is a known bug in Outlook Express. Microsoft is aware of the
      problem and its cause. They have informed us that they do not have any
      plans to fix it at the present time.

      <p>The problem is also reported in Outlook 2000, but not verified.</p>

      <p>Outlook Express uses the IMAP IDLE command to avoid having to "ping"
      the server every few minutes for new mail. Unfortunately, Outlook
      Express overlooks the part in the IDLE specification which requires
      that a client terminate and restart the IDLE before the IMAP 30 minute
      inactivity autologout timer triggers.</p>

      <p>When this happens, Outlook Express displays "Not connected" at the
      bottom of the window. Since it's no longer connected to the IMAP
      server, it isn't going to notice any new mail.</p>

      <p>As soon as the user does anything that would cause an IMAP
      operation, Outlook Express will reconnect and new mail will flow again.
      If the user does something that causes an IMAP operation at least every
      29 minutes, the problem won't happen.</p>

      <p>Modern versions of imapd attempt to work around the problem by
      automatically reporting fake new mail after 29 minutes. This causes
      Outlook Express to exit the IDLE state; as soon as this happens imapd
      revokes the fake new mail. As long as this behavior isn't known to
      cause problems with other clients, this workaround will remain in
      imapd.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.38"><strong>7.38 Why don't I get any new mail notifications from
     Entourage?</strong></a></p>

  <dl>
    <dd>
      This is a known bug in Entourage.

      <p>You built an older version of imapd with the
      <strong>MICROSOFT_BRAIN_DAMAGE</strong> option set, in order to disable
      support for the IDLE command. However, Entourage won't get new mail
      unless IDLE command support exists.</p>

      <p>Note: the MICROSOFT_BRAIN_DAMAGE option no longer exists in modern
      versions, as the Outlook Express problem which it attempted to solve
      has been worked around in another way.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.39"><strong>7.39 Why doesn't Entourage work at
     all?</strong></a></p>

  <dl>
    <dd>
      It's hard to know. Entourage breaks almost every rule in the book for
      IMAP. It is highly instructive to do a packet trace on Entourage, as an
      example of how <em>not</em> to use IMAP. It does things like STATUS
      (MESSAGES) on the currently selected mailbox and re-fetching the same
      static data over and over again.

      <p>It seems that every time we understand what it is doing wrong in
      Entourage and come up with a workaround, we learn about something else
      that's broken.</p>

      <p>Try building imapd with the <strong>ENTOURAGE_BRAIN_DAMAGE</strong>
      option set, in order to disable the diagnostic that occurs when doing
      STATUS on the currently selected mailbox.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.40"><strong>7.40 Why doesn't Netscape Notify (NSNOTIFY.EXE) work
     at all?</strong></a></p>

  <dl>
    <dd>
      This is a bug in NSNOTIFY; it doesn't handle unsolicited data from the
      server correctly.

      <p>Fortunately, there is no reason to use this program with IMAP;
      NSNOTIFY is a polling program to let you know when new mail has
      appeared in your maildrop. This is necessary with POP; but since IMAP
      dynamically announces new mail in the session you're better off (and
      will actually cause less load on the server!) keeping your mail reading
      program's IMAP session open and let IMAP do the notifying for you.</p>

      <p>Consequently, the recommended fix for the NSNOTIFY problem is to
      delete the NSNOTIFY binary.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.41"><strong>7.41 Why can't I connect via SSL to Eudora? It says
     the connection has been broken, and in the server syslogs I see "Command
     stream end of file".</strong></a></p>

  <dl>
    <dd>There is a report that you can fix the problem by going into Eudora's
    advanced network configuration menu and increasing the network buffer
    size to 8192.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.42"><strong>7.42 Sheesh. Aren't there <em>any</em> good IMAP
     clients out there?</strong></a></p>

  <dl>
    <dd>
      Yes!

      <p>Pine is a <em>wonderful</em> client. It's fast, it uses IMAP well,
      and it generates text mail (life is too short to waste on HTML mail).
      Also, there are some really wonderful things in progress in the Pine
      world.</p>

      <p>There are some good GUI clients out there, mostly from smaller
      vendors. Without naming names, look for the vendors who are active in
      the IMAP protocol development community, and their products.</p>

      <p>Netscape, Eudora, and Outlook <em>can</em> be configured with enough
      effort to be good citizens and work well for users, <em>but</em> they
      can also be badly misconfigured, and often the misconfiguration is the
      default.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.43"><strong>7.43 But wait! PC Pine (or other PC program build with
     c-client) crashes with the message</strong> <tt>incomplete SecBuffer
     exceeds maximum buffer size</tt> <strong>when I use SSL connections.
     This is a bug in c-client, right?</strong></a></p>

  <dl>
    <dd>
      It's a bug in the Microsoft SChannel.DLL, which implements SSL.
      Microsoft admits it (albeit with an unstatement: "it's not fully RFC
      compliant"). The problem is that SChannel indicates that the maximum
      SSL packet data size is 5 bytes smaller than the actual maximum. Thus,
      any IMAP server which transmits a maximum sized SSL packet will not
      work with PC Pine or any other program which uses SChannel.

      <p>It can take a while for the problem to show up. The client has to do
      something that causes at least 16K of contiguous data. Many clients do
      partial fetching, which tends to reduce the number of cases where this
      can happen. However, <em>all</em> software which uses SChannel to
      support SSL is affected by this bug.</p>

      <p>This problem does not affect UNIX code, since OpenSSL is used on
      UNIX.</p>

      <p>This problem most recently showed up with the CommunigatePro IMAP
      server. They have an update which trims down their maximum contiguous
      data to less than 16K, in order to work around the problem.</p>

      <p>This problem has also shown up with the Exchange IMAP server with
      UNIX clients (including Pine built with an older version of c-client)
      which sends full-sized 16K SSL packets. Modern c-client works around
      the problem by trimming down its maximum outgoing SSL packet size to
      8K.</p>

      <p>Microsoft has developed a hotfix for this bug. Look up MSKB article
      number 300562. Contrary to the article text which implies that this is
      a Pine issue, this bug also affect Microsoft Exchange server with *any*
      UNIX based client that transmits full-sized SSL payloads.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.44"><strong>7.44 My qpopper users keep on getting the DON'T DELETE
     THIS MESSAGE -- FOLDER INTERNAL DATA if they also use Pine or IMAP. How
     can I fix this?</strong></a></p>

  <dl>
    <dd>
      This is an incompatibility between qpopper and the c-client library
      used by Pine, imapd, and ipop[23]d.

      <p>Assuming that you want to continue using qpopper, look into
      qpopper's <strong>--enable-uw-kludge-flag</strong> configuration flag,
      which is documented as "check for and hide UW 'Folder Internal Data'
      messages".</p>

      <p>The other alternative is to switch from qpopper to ipop3d.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.45"><strong>7.45 Help! I installed the servers but I can't connect
     to them from my client!</strong></a></p>

  <dl>
    <dd>
      Review the installation instructions carefully. Make sure that you have
      not skipped any of the steps. Make sure that you have made the correct
      entries in the configuration files; pay careful attention to the exact
      spelling of the service names and the path names. Make sure as well
      that you have properly restarted inetd.

      <p>If you have a system with Yellow Pages/NIS such as Solaris, have you
      updated the service names there as well as in /etc/services?</p>

      <p>If you have a system with TCP wrappers, have you properly updated
      the TCP wrapper files (e.g. /etc/hosts.allow and /etc/hosts.deny) for
      the servers?</p>

      <p>If you have a system which uses xinetd instead of inetd, have you
      made sure that you have made the correct corresponding xinetd changes
      for those services?</p>

      <p>Try telneting to the server port (143 for IMAP, 110 for POP3). If
      you get a "refused" error, that probably means that you don't have the
      service set up in inetd.conf. If the connection opens and then closes
      with no message, the service is set up, but either the path name of the
      server binary in inetd.conf is wrong or your TCP wrappers are
      configured to deny access.</p>

      <p>If you don't know how to make the corresponding changes to these
      files, seek the help of a local expert for your system.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.46"><strong>7.46 Why do I get the message</strong> <tt>Can not
     authenticate to SMTP server: 421 SMTP connection went away!</tt>
     <strong>and why did this happen? There was also something about</strong>
     <tt>SECURITY PROBLEM: insecure server advertised AUTH=PLAIN</tt></a></p>

  <dl>
    <dd>
      Some versions of qmail, including that running on mail.smtp.yahoo.com,
      disconnect the SMTP session if you fail to authenticate prior to
      attempting to transmit mail. An attempt to authenticate was made, but
      it failed because the server had already disconnected.

      <p>To work around this, you need to specify /user=... in the host name
      specification.</p>

      <p>The SECURITY PROBLEM came about because the server advertised the
      AUTH=PLAIN SASL authentication mechanism outside of a TLS-encrypted
      session, in violation of RFC 4616. This message is just a warning, and
      in fact occurred after the server had disconnected.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.47"><strong>7.47 Why do I get the message</strong> <tt>SMTP
     Authentication cancelled</tt> <strong>and why did this happen? There was
     also something about</strong> <tt>SECURITY PROBLEM: insecure server
     advertised AUTH=PLAIN</tt></a></p>

  <dl>
    <dd>
      This is a bug in the SMTP server.

      <p>Some versions of qmail, including that running on
      mail.smtp.yahoo.com, have a bug in their implementation of SASL in
      their SMTP server, which renders it non-compliant with the
      standard.</p>

      <p>If the client does not provide an initial response in the command
      line for an authentication mechanism whose profile does not have an
      initial challenge, qmail issues a bogus response:</p>
      <pre>
 334 ok, go on
</pre>The problem is the "ok, go on". This violates RFC 4954's requirement
that the text part in a 334 response be a BASE64 encoded string; in other
words, it is a protocol syntax error.

      <p>In the case of AUTH=PLAIN, RFC 4422 (page 7) requires that the
      encoded string have no data. In other words, the appropropiate
      standards-compliant server response is "334" followed by a SPACE and a
      CRLF.</p>

      <p>The SECURITY PROBLEM came about because the server advertised the
      AUTH=PLAIN SASL authentication mechanism outside of a TLS-encrypted
      session, in violation of RFC 4616. This message is just a warning, and
      is not related the "Authentication cancelled" problem.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="7.48"><strong>7.48 Why do I get the message</strong> <tt>Invalid
     base64 string</tt> <strong>when I try to authenticate to a Cyrus
     server?</strong></a></p>

  <dl>
    <dd>
      This slightly misleading message is the way that a Cyrus server
      indicates that an authentication exchange was cancelled. It is not
      indicative of a bug or protocol violation.

      <p>The most common reason that this happens is if the Cyrus server
      offers Kerberos authentication, c-client is built with Kerberos
      support, but your client system is not within the Kerberos realm. In
      this case, the client code will try to authenticate via Kerberos, fail
      to get the Kerberos credentials, cancel the authentication attempt, and
      try the next available authentication technology.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><br></p>

  <h2><a name="additional">8. Where to Go For Additional Information</a></h2>
  <hr>

  <p><a name="8.1"><strong>8.1 Where can I go to ask questions?</strong></a><br>
  <a name="8.2"><strong>8.2 I have some ideas for enhancements to IMAP. Where
     should I go?</strong></a></p>

  <dl>
    <dd>
      If you have questions about the IMAP protocol, or want to participate
      in discussions of future directions of the IMAP protocol, the
      appropriate mailing list is imap-protocol@u.washington.edu. You can
      subscribe to this list via <a href=
      "mailto:imap-protocol-request@u.washington.edu"><tt>imap-protocol-request@u.washington.edu</tt></a>

      <p>If you have questions about this software, you can send me email
      directly or use the imap-uw@u.washington.edu mailing list. You can
      subscribe to this list via <a href=
      "mailto:imap-uw-request@u.washington.edu"><tt>imap-uw-request@u.washington.edu</tt></a></p>

      <p>If you have general questions about the use of IMAP software
      (not specific to the UW IMAP toolkit) use the
      imap-use@u.washington.edu mailing list. You can subscribe to
      this list via <a href=
      "mailto:imap-use-request@u.washington.edu"><tt>imap-use-request@u.washington.edu</tt></a></p>

      <p>You must be a subscriber to post to these lists.  As an
      alternative, you can use the
      <strong>comp.mail.imap</strong> newsgroup.</p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="8.3"><strong>8.3 Where can I read more about IMAP and other email
     protocols?</strong></a></p>

  <dl>
    <dd>We recommend <em>Internet Email Protocols: A Developer's Guide</em>,
    by Kevin Johnson, published by Addison Wesley, ISBN 0-201-43288-9.</dd>
  </dl>

  <p><a href="#top">Back to top</a></p>
  <hr>

  <p><a name="8.4"><strong>8.4 Where can I find out more about setting up and
     administering an IMAP server?</strong></a></p>

  <dl>
    <dd>
      We recommend <em>Managing IMAP</em>, by Dianna Mullet &amp; Kevin
      Mullet, published by O'Reilly, ISBN 0-596-00012-X.

      <p>This book also has an excellent comparison of the UW and Cyrus IMAP
      servers.<br></p>
    </dd>
  </dl>

  <p><a href="#top">Back to top</a></p>

  <p>Last Updated: 15 November 2007</p>

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