Installing and configuring the IMAP Server

Installing and configuring the IMAP Server

This section describes the shell scripts to run and the configuration files to modify once "configure" and "make" have run.
  1. Create a user and group for the Cyrus subsystem. The examples in this document assume a user of "cyrus" and a group of "mail", though any user and group name can be used. If a user other than "cyrus" is to be used, it must have been previously specified in the "--with-cyrus-user=" option to "configure". If a group other than "mail" is to be used, it must have been previously specified in the "--with-cyrus-group=" option to "configure".

  2. After you've logged in as "root", install the cyrus software.
       make install
    
    Be sure that the server programs ended up in the directory specified by "--with-cyrus-prefix" (by default, "/usr/cyrus/bin").

  3. The Cyrus IMAP server uses the 4.3BSD syslog that separates messages into both levels and categories. Invoke "man syslog" to see if "openlog()" takes three arguments. If it does not, replace the system "syslogd" and "syslog.conf" with the files provided in the "syslog" directory.
       mv syslogd /etc/syslogd
       mv syslog.conf /etc/syslog.conf
    
    If you do not copy the "syslog/syslog.conf" file to the "/etc" directory, be sure to add support for "local6.debug". The file should include a line like:
       local6.debug  /var/log/imapd.log
    
    You probably also want to log SASL messages with a line like:
       auth.debug /var/log/auth.log
    
    After installation and testing, you probably want to change the ".debug" component to something a little less verbose. Create the log files:
       touch /var/log/imapd.log /var/log/auth.log
    
  4. Create the file "/etc/imapd.conf". Here is a sample "imapd.conf" with a minimal number of values defined:
       configdirectory: /var/imap
       partition-default: /var/spool/imap
       admins: curtj abell
       sasl_pwcheck_method: saslauthd
    
    For a description of all the fields in this file, see the imapd.conf(5) man page. (Note that this file also exports values to libsasl, the most important of them the pwcheck_method. In this example, users are authenticated via the saslauthd daemon, which can be run in a number of different ways.)

    READ THE imapd.conf(5) MAN PAGE. There are options in there that you will want to know about and default behavior that you may not like.

    Note that everyday users should not be administrators. Admins have powers not granted to regular users and while the server allows them to receive mail, some problems will occur if admins are used as regular users. You also should not read mail as an administrator. You should have separate accounts for reading mail and administrating. This is especially true if using the altnamespace option, because admins are always presented with the standard (internal) namespace.

  5. Create the configuration directory specified by the "configdirectory" option in "imapd.conf." The configuration directory is similar in concept to the "/usr/lib/news" directory. It stores information about the IMAP server as a whole.

    This document uses the configuration directory "/var/imap" in its examples. This directory should be owned by the cyrus user and group and should not permit access to other users.

       cd /var
       mkdir imap
       chown cyrus imap
       chgrp mail imap
       chmod 750 imap
    
  6. Create the default partition directories specified in the "/etc/imapd.conf" file.

    This document uses a default partition directory of "/var/spool/imap" in the following example:

       cd /var/spool
       mkdir imap
       chown cyrus imap
       chgrp mail imap
       chmod 750 imap
    
    The partition directory is similar in concept to /var/spool/news. It is where the mailboxes are stored. Unlike most netnews systems, Cyrus allows you to have more than one partition.
  7. If you wish to use Sieve, and you didn't configure deliver to look in home directories (see the imapd.conf man page), create the Sieve directory:
       cd /usr
       mkdir sieve
       chown cyrus sieve
       chgrp mail sieve
       chmod 750 sieve
    
  8. Change to the Cyrus user and use the tool "tools/mkimap" to create the rest of the directories (subdirectories of the directories you just created).
       su cyrus
       tools/mkimap
       exit
    
    
    If Perl is not available, it should be easy (but time consuming) to create these directories by hand.

  9. LINUX SYSTEMS USING EXT2FS ONLY: Set the user, quota, and partition directories to update synchronously. Failure to do this may lead to data corruption and/or loss of mail after a system crash. Unfortunately, doing so may result in a serious performance hit. If you are using a newer filesystem than ext2fs on Linux, this step should not be necessary. (Running ext3 in any mode is safe.)
       cd /var/imap
       chattr +S user quota user/* quota/*
       chattr +S /var/spool/imap /var/spool/imap/*
    
    Also set the queue directory of the mail daemon to update synchronously. The following example is for sendmail:
       chattr +S /var/spool/mqueue
    

  10. To enable STARTTLS support, see how to configure OpenSSL below.

  11. Add the following lines to the "/etc/services" file if they aren't already there.
       pop3      110/tcp
       nntp      119/tcp
       imap      143/tcp
       imsp      406/tcp
       nntps     563/tcp
       acap      674/tcp
       imaps     993/tcp
       pop3s     995/tcp
       kpop      1109/tcp
       lmtp      2003/tcp
       sieve     4190/tcp
       fud       4201/udp
    

  12. Remove "/etc/[x]inetd.conf" entries. Any imap, imaps, pop3, pop3s, kpop, lmtp and sieve lines need to be removed from /etc/[x]inetd.conf and [x]inetd needs to be restarted.

Configuring the Master Process

  1. Choose a configuration from the master/conf directory:
    small.conf
    bare-bones server supporting IMAP and POP
    normal.conf
    server supporting IMAP, POP, the SSL wrapped versions, and the Sieve script management protocol
    prefork.conf
    The same configuration as above, but with some preforked processes for faster processing.
    backend-cmu.conf
    Our configuration (for Murder Backend / typical IMAP servers)
    frontend-cmu.conf
    Our configuration (for Murder Frontend servers)

    To use normal.conf, do:

       cp master/conf/normal.conf /etc/cyrus.conf
    

    Optionally, you can edit /etc/cyrus.conf to disable or enable certain services, or to tune the number of preforked copies. Be sure not to remove the entries that are labeled required.

  2. Arrange to start "/usr/cyrus/bin/master" as root when the system starts. It will bind some ports and then give up its root privileges. Until your system reboots, you can start the master process by hand:
       /usr/cyrus/bin/master &
    

  3. Monitor the progress of the master process by examining the imapd.log file. It should never exit by itself, but you can shut down the mail system by sending it a signal with kill.

  4. Clean Shutdown - you can shut the master process down cleanly by sending it a SIGQUIT rather than SIGTERM signal. This will cause the master process to send SIGQUIT to all its children and then wait for them to finish cleanly. This avoids issues like a message being appended by lmtpd but the sync_log record never being written.

    Since a clean shutdown may never finish if a child process is stuck for some reason the recommended approach is to send a SIGQUIT then loop on the master process sending a signal 0 every second until either the master process has gone away or a suitable time has expired (maybe 10 seconds). You can then send a SIGTERM if the process still exists.

    At FastMail the following snippet of perl is used (warning: Linux specific signal numbers - check your own system before using this):

        my $pid = `cat $PIDFILE`;
        chomp($pid);
        print "Trying nice shutdown - killing $pid with SIGQUIT\n";
        kill 3, $pid;
        foreach my $num (1..10) {
          if (kill 0, $pid) {
            print "Not dead yet after $num seconds\n";
            sleep 1;
          }
          else {
            last;
          }
        }
        if (kill 0, $pid) {
          print "No more Mr. Nice Guy - killing $pid with SIGTERM\n";
          kill 15, $pid;
        }
    

Configuring the Mail Transfer Agent

In order to deliver mail to the Cyrus system, you'll have to configure your MTA (Sendmail, Postfix, Exim, etc.) to use LMTP.

Configuring Sendmail

Generate a sendmail configuration file which delivers local mail to the IMAP server. See the file cf/README in the Sendmail distribution for information on how to create a complete configuration file. This file also lists variables that can be used to customize the mailer definitions mentioned below.

The following configurations assume that you are using the lmtpunix service from one of the sample cyrus.conf files discussed above.

  • For Sendmail 8.12.4 and higher, use the cyrusv2 mailer definition in the Sendmail distribution:
    define(`confLOCAL_MAILER', `cyrusv2')
    MAILER(`cyrusv2')
    
    If you wish to change the name of the UNIX socket or switch to TCP, define CYRUSV2_MAILER_ARGS appropriately as described in cf/README.
  • For Sendmail 8.10 - 8.12.3, use the cyrusv2.mc file as a template to create a Sendmail configuration file.
  • For Sendmail 8.9.x and earlier, use the cyrus mailer definition in the Sendmail distribution:
    define(`confLOCAL_MAILER', `cyrus')
    MAILER(`cyrus')
    
    Edit /etc/group and add user "daemon" to the "mail" group. This will permit sendmail to run the "deliver" (LMTP client) program to deliver mail to the IMAP server.

Cyrus also includes a socket map daemon smmapd which can be used by Sendmail 8.13 and higher (a patch for 8.12 is available) to verify at RCPT TO time that a message can be delivered to the particular mailbox. To use this daemon, add smmapd as a service in cyrus.conf and configure Sendmail accordingly.

Configuring Postfix

The Postfix source distribution comes with the file "README_FILES/LMTP_README". Even if you are using a binary distribution of Postfix, it would be well worth your while to download the full Postfix source. Not only will you get the above file, but numerous other "readme" files and sample configuration files.

One thing you need to watch out for is the UID and GID of the Postfix software. As it states in the Postfix "INSTALL" document, you must create a new account that does not share its UID and GID with any other user account. This is for security reasons. If you installed Postfix with a GID of "mail", you will need to select a different GID for Cyrus. See the Cyrus configure options "--with-cyrus-user" and "--with-cyrus-group". (This was more crucial when the use of Cyrus' "deliver" was more prevalent, but it is still a good idea to follow this policy.)

Another thing to note is the location of your "sendmail" command. On some platforms this will be "/usr/sbin/sendmail", on others, "/usr/lib/sendmail". Cyrus will need to know where this command is. See Installing Sieve for more details.

Assuming that you are using the lmtpunix service from one of the sample cyrus.conf files discussed above, the Postfix configuration file "/etc/postfix/main.cf" should have the following line:

  mailbox_transport = lmtp:unix:/var/imap/socket/lmtp

Naturally, both the Postfix UID and the Cyrus UID need to be able to access the specified socket file.

Starting with Postfix snapshot-20010222, you can improve the efficiency of LMTP delivery via the "mailbox_transport" by putting the following entries in "/etc/postfix/main.cf":

  local_destination_recipient_limit = 300
  local_destination_concurrency_limit = 5

Of course you should adjust these settings as appropriate for the capacity of the hardware you are using. The recipient limit setting can be used to take advantage of the single instance message store capability of Cyrus. The concurrency limit can be used to control how many simultaneous LMTP sessions will be permitted to the Cyrus message store.

Additional examples are included in the Postfix file "README_FILES/LMTP_README".

Configuring Exim 4

Generate an Exim configuration file which delivers local mail to the IMAP server. See the Exim documentation for information on how to create a complete configuration file.

Cyrus is designed to be used as a black-box server -- there are usually no local user accounts. As a result, you must define the following "router":

localuser:
  driver = accept
  transport = local_delivery

The following "transports" assume that you are using either the lmtpunix or lmtp service from one of the sample cyrus.conf files discussed above.

  • Using lmtpunix (UNIX socket):
    local_delivery:
      driver = lmtp
      command = "/usr/cyrus/bin/deliver -l"
      batch_max = 20
      user = cyrus
    
  • Using lmtp (TCP socket -- Exim and Cyrus on same host):
    local_delivery:
      driver = smtp
      protocol = lmtp
      hosts = localhost
      allow_localhost
    

For more advanced configurations (such as address verification, etc), consult the Exim documentation and sample configurations.

Exporting Netnews via IMAP

If you wish to use export Netnews via IMAP, consult install-netnews.php.

SSL, TLS, and OpenSSL

Transport Layer Security (TLS), is a standardized version of the Secure Sockets Layer (SSL v3) standard. IMAP can make use of two different versions of TLS/SSL: STARTTLS and an SSL wrapped session.

In STARTTLS, a client connects to the IMAP port as normal and then issues the STARTTLS command, which begins a TLS negotiation. This is currently supported by the Cyrus IMAP server when it is compiled with OpenSSL.

The alternative, a SSL wrapped connection, involves the client connected to a seperate port ("imaps") and negotiating a SSL session before starting the IMAP protocol. Again, this is supported natively by the Cyrus IMAP server when it is compiled with OpenSSL.

Both TLS and SSL require a server key and a certificate. Optionally, in addition to establishing a secure connection, TLS can authenticate the client.

Configuring Cyrus with OpenSSL

  1. OpenSSL requires the certificate and key in PEM format. You can create the server's private key and certificate yourself using OpenSSL. Here, we create a self-signed key for the machine "foobar.andrew.cmu.edu" and put both the certificate and key in the file "/var/imap/server.pem".

    Please do not blindly enter in the information to OpenSSL below. Instead, enter the appropriate information for your organization (i.e., NOT Carnegie Mellon University for the Organization Name, etc.).

    openssl req -new -x509 -nodes -out /var/imap/server.pem -keyout /var/imap/server.pem -days 365
    Using configuration from /usr/local/lib/openssl/openssl.cnf
    Generating a 1024 bit RSA private key
    .............+++++
    ......................+++++
    writing new private key to '/var/imap/server.pem'
    -----
    You are about to be asked to enter information that will be incorporated
    into your certificate request.
    What you are about to enter is what is called a Distinguished Name or a DN.
    There are quite a few fields but you can leave some blank
    For some fields there will be a default value,
    If you enter '.', the field will be left blank.
    -----
    Country Name (2 letter code) [AU]:US
    State or Province Name (full name) [Some-State]:Pennsylvania
    Locality Name (eg, city) []:Pittsburgh
    Organization Name (eg, company) [Internet Widgits Pty Ltd]:Carnegie Mellon University
    Organizational Unit Name (eg, section) []:Andrew Systems Group
    Common Name (eg, YOUR name) []:foobar.andrew.cmu.edu
    Email Address []:
    
  2. Make sure to make key file(s) readable by the Cyrus user. For example: chown cyrus /var/imap/server.pem
  3. Add the following to /etc/imapd.conf to tell the server where to find the certificate and key files (used for ALL services):
    server_cert_file: /var/imap/server.cert
    server_key_file: /var/imap/server.key
    
    Optionally, you can use separate certificates and key files for each service:
    [servicename]_server_cert_file: /var/imap/imap-server.cert
    [servicename]_server_key_file: /var/imap/imap-server.key
    
    "servicename" here refers to the name of the service as specified in cyrus.conf. It is not necessarily the name of the binary.

    This is useful if you want to use different hostnames for each service (e.g., via virtual host interfaces or DNS CNAMEs). In the absence of any of the service specific options, the value of the global option is used. A value of disabled for the certificate or key file for a particular service will disable SSL/TLS for that service.

    If you have a Certificate Authority (CA), you may wish to generate a certificate request and send it to be signed by your CA.

    By default, Cyrus will cache SSL/TLS sessions for reuse for up to 24 hours. By adjusting the value of the tls_session_timeout option in imapd.conf, the session caching can be disabled (0) or the expiration period shortened.

  4. You can test STARTTLS by using imtest:
    imtest -t "" foobar.andrew.cmu.edu
    

Client-side certificates

Client certificates are somewhat harder to configure than server certificates. You'll need a CA (certificate authority) and need to generate client certificates signed by that CA. STARTTLS in Sendmail and other MTAs have similiar problems, so Claus Assman's page is a good reference.

You can use the self-signed certificate generated above as a CA for client certificates. To do this, try the following:

TODO: write me!

Unfortunately, there's no standard on how to convert the client's authenticate DN (distinguished name) to a SASL authentication name.

Alternate Namespace and UNIX Hierarchy Convention

If you wish to use the alternate namespace and/or the UNIX hierarchy convention, consult altnamespace.php.


last modified: $Date: 2010/01/06 17:01:29 $