For scalability, we are going to arrange for exim to deliver all
local mail in Maildir format. This creates a subdirectory called
"Maildir" in the user's home directory, which in turn
contains three subdirectories: new,
cur and tmp.
Messages are written into tmp,
moved to new when
delivery is complete, and moved to cur
when read. Each message has a long unique filename based on the
hostname and the time of day.
From the Courier IMAP web site, “The primary advantage of maildirs is that multiple applications can access the same Maildir simultaneously without requiring any kind of locking whatsoever. Maildir is a faster and more efficient way to store mail. It works particularly well over NFS, which has a long history of locking-related woes.
Exim does not include any software for retrieving mail from a mailbox, so we need to install additional software. Courier is a mail system which includes a number of packages. In fact it has its own MTA, but we will ignore this.The components we are interested in are the IMAP and POP3 servers.
You can get the entire courier system as one package (including the MTA), or just the components. We will get the authlib and pop3/imap components separately.
Remember: in the command examples given below, commands shown with the prompt "$" should be run as your normal non-root userid. Only those commands with prompt "#" need to be run as root.
Edit /usr/local/etc/exim/configure,
find the local_delivery
transport and modify it as follows:
local_delivery: driver = appendfile directory = $home/Maildir maildir_format maildir_use_size_file #file = /var/mail/$local_part delivery_date_add envelope_to_add (Continues on next page==>) return_path_add group = mail #user = $local_part mode = 0660 no_mode_fail_narrower
Optionally you could add further parameters to this transport which let you impose quotas on your users, for example to limit all users to 100 megabytes of storage each:
maildir_tag = ,S=$message_size quota_size_regex = ,S=(\d+) quota = 100M quota_warn_threshold = 90%
(Aside: this quota mechanism relies on users not meddling with the quota information which is stored within their maildir; in other words, users with shell access would be able to bypass their quota if they knew what they were doing)
Remember to HUP your exim daemon.
# cat
/var/run/exim.pid
# kill -HUP nnnn
Now test out your new configuration by delivering to some local account on your machine. You may want to do these exercises using one terminal logged in as root and another as a user account. Then you can quickly go back and forth using (for example) ALT-CTRL-F1 and ALT-CTRL-F2. Note that “localuser” is the username that you are using for testing:
$ /usr/local/sbin/exim -bt localuser localuser@pcnn.e0.ws.afnog.org router = localuser, transport = local_delivery $ /usr/local/sbin/exim localuser Here is a test . $ cd /home/localuser/Maildir $ ls cur new tmp $ ls new 102078119.7969.pcnn.e0.ws.afnog.org,S=426 $ cat new/* Return-path: <root@pcnn.e0.ws.afnog.org> ... Here is a test
Note: once you have changed to Maildir delivery, you will find that any local Unix MUA (which looks for new messages in /var/mail/username) will no longer see your incoming mail. How to fix this depends on which MUA you are using. Some examples:
mutt
Edit/usr/local/etc/Muttrcand put:
set spoolfile="~/Maildir/" pine
pine
Not supported by default, patch available. http://www.math.washington.edu/~chappa/pine/info/maildir.html
kmail
Has direct access to /var/mail or Maildir directly; can also use POP3/IMAP to retrieve new mail.
You can get the entire courier system as one package (including the MTA), or just the components. We will get the authlib and the pop3/imap components separately.
As with most software packages under FreeBSD, you have a choice of
installing directly from source, or using the ports system. If you
install from source you have the most control over which version is
installed and which compilation options are used. However installing
from packages is easier, gives you a record of which files where
installed where, and installs the files in the "normal"
places you'd expect for a FreeBSD system. In particular, the commands
get installed in /usr/local/bin
and /usr/local/sbin,
which is already in your $PATH. We will use the ports in this lab.
The courier packages now share a single authentication library, courier-authlib. This package is responsible for looking up usernames and passwords - it can retrieve this information from various locations, including Unix system accounts (authpam), SQL databases (authmysql and authpgsql), LDAP databases (authldap), and local file databases (authuserdb). Having a separate package means that the same authentication configuration can now be shared by both POP3/IMAP and Webmail.
# portinstall courier-authlib
When prompted for options on the screen, press the down arrow to highlight the option:
[X] AUTH_USERDB Userdb support
Press <TAB> to highlight OK, and then <ENTER> to continue.Total compile time on your machines will be between around 10 minutes.
courier-authlib runs a pool of authentication daemons which
perform the actual work; courier-imap and SquirrelMail communicate
with these daemons via a socket. So the next thing we need to do is
to start the daemons. First you need to edit /etc/rc.conf:
# vi /etc/rc.conf add the following line: courier_authdaemond_enable="YES"
Courier-authlib itself has a single configuration file,
/usr/local/etc/authlib/authdaemonrc.
For the purposes of this exercise, we will turn on
authentication debugging. In “vi” a shortcut to find something is
to press “/” and the text you wish to locate.
# cd /usr/local/etc/authlib # vi authdaemonrc change this line: DEBUG_LOGIN=0 to: DEBUG_LOGIN=1
Continue to edit the authdaemonrc file. To save resources, you can also configure the authdaemond process not to try any authentication mechanisms which you know you don't need. For example, if all your authentication is only via PAM for Unix system passwords, then you can remove all the others. Save the original line so that your the following changes look like this:
#authmodulelist="authuserdb authvckpw authpam authldap authmysql authpgsql" authmodulelist="authpam"
Now we are ready to start the authentication daemons:
# /usr/local/etc/rc.d/courier-authdaemond.sh start Starting courier_authdaemond. # ps auxwww | grep authdaemond root 36787 0.0 0.2 1220 720 p1 S 10:40AM 0:00.00 /usr/local/sbin/courierlogger -pid=/usr/local/var/spool/authdaemon/pid -start /usr/local/libexec/courier-authlib/authdaemond root 36788 0.0 0.2 1464 880 p1 S 10:40AM 0:00.00 /usr/local/libexec/courier-authlib/authdaemond root 36789 0.0 0.2 1464 880 p1 S 10:40AM 0:00.00 /usr/local/libexec/courier-authlib/authdaemond root 36790 0.0 0.2 1464 880 p1 S 10:40AM 0:00.00 /usr/local/libexec/courier-authlib/authdaemond root 36791 0.0 0.2 1464 880 p1 S 10:40AM 0:00.00 /usr/local/libexec/courier-authlib/authdaemond root 36792 0.0 0.2 1464 880 p1 S 10:40AM 0:00.00 /usr/local/libexec/courier-authlib/authdaemond root 36793 0.0 0.2 1464 880 p1 S 10:40AM 0:00.00 /usr/local/libexec/courier-authlib/authdaemond
ps shows one courierlogger process, and six authdaemond processes (one master, five workers). If you didn't see "Starting courier_authdaemond" then you made a typing error.
You can test the authentication system by itself; the "authtest" command sends requests down the authentication socket, and displays the responses which come back. Test using any Unix login account which already exists on your system.
# rehash -- to ensure your shell sees this new command # authtest inst -- find an account called 'brian' # authtest inst <password> -- check 'brian' has password 'foo' # authenumerate -- list all accounts
Try it also with a non-existent username, and with both the right password and a wrong password for an account, to confirm that passwords are being validated properly.
Because we enabled login debugging, you should find that each
authentication request generates detailled information in
/var/log/debug.log
showing how the request is passed to each module in turn. Have a look
in this file to confirm:
# less /var/log/debug.log
Further documentation for courier-authlib can be found on the web at
http://www.courier-mta.org/authlib/,
and is also installed in:/usr/local/share/doc/courier-authlib/
Using ports, building courier-imap is straightforward:
# portinstall courier-imap [When prompted for options on the screen, press <TAB> to highlight OK, and then <ENTER> to continue.]
Compilation will take around 10 minutes on your machines.
You can choose to run POP3, IMAP, or both. There is a configuration file for each one:
/usr/local/etc/courier-imap/pop3d /usr/local/etc/courier-imap/imapd
The default configuration is acceptable in most cases. However for a large server you may wish to increase the maximum number of concurrent connections from the default of 40, if you have fairly powerful hardware:
# cd /usr/local/etc/courier-imap # vi pop3d ... MAXDAEMONS=300 ... # vi imapd ... MAXDAEMONS=300 ...
Then, you need to enable the daemon(s) which you wish to run in
/etc/rc.conf
# vi /etc/rc.conf add the following line(s): courier_imap_pop3d_enable="YES" courier_imap_imapd_enable="YES"
And then run the startup script(s):
# /usr/local/etc/rc.d/courier-imap-pop3d.sh start Starting courier_imap_pop3d. # /usr/local/etc/rc.d/courier-imap-imapd.sh start Starting courier_imap_imapd.
Test using telnet: POP3 and IMAP are both text-based layer 7 protocols and you can drive them by hand.
# telnet localhost 110 Connected to localhost.ws.afnog.org Escape character is '^]'. +OK Hello there. user username +OK Password required. pass password +OK logged in. stat +OK 26 49857 retr 1 +OK 1073 octets follow. ... message . quit +OK Bye-bye. Connection closed by foreign host. # telnet localhost 143 Connected to localhost.ws.afnog.org. Escape character is '^]'. * OK [CAPABILITY IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE ACL ACL2=UNION STARTTLS] Courier-IMAP ready. Copyright 1998-2005 Double Precision, Inc. See COPYING for distribution information. a login username password a OK LOGIN Ok. a examine inbox * FLAGS (\Answered \Flagged \Deleted \Seen \Recent) * OK [PERMANENTFLAGS ()] No permanent flags permitted * 26 EXISTS * 0 RECENT * OK [UIDVALIDITY 989061119] Ok * OK [READ-ONLY] Ok a logout * BYE Courier-IMAP server shutting down a OK LOGOUT completed Connection closed by foreign host.
NOTE: The daemons will fail to login if the mail directory
does not exist, although current versions do now provide an error
message. Hence you need to have delivered at least one message to the
user, to create their mailbox, before they can login (or use the
'maildirmake' command to create it). Look for logging messages in
/var/log/maillog
and /var/log/debug.log.
If you wish, you can choose to allow pop3 over SSL (port 995) and imap over SSL (port 993). The advantage is that, for clients which support it, the traffic is encrypted. In this day and age this is almost a requirement for any sane mail server. Allowing connections to pop or imap over unencrypted ports is no longer a viable solution. The disadvantage is higher CPU load on your server for the encryption of data.
To run SSL you will need a certificate. For testing purposes you
can use a 'self-signed' certificate. The pop3d.cnf
and imapd.cnf files contain the
parameters for the Snakeoil certificate. You may edit this for
you environment, but note that it is not proper certificate signed by
a recognised CA.
Run the following scripts which will generate
them for you:
# cd /usr/local/etc/courier-imap # cp pop3d.cnf.dist pop3d.cnf # cp imapd.cnf.dist imapd.cnf # mkpop3dcert # mkimapdcert
Next, enable the SSL daemons in /etc/rc.conf:
# vi /etc/rc.conf courier_imap_pop3d_ssl_enable="YES" # pop3 over ssl, port 995 courier_imap_imapd_ssl_enable="YES" # imap over ssl, port 993
Then you start the servers:
# /usr/local/etc/rc.d/courier-imap-pop3d-ssl.sh start Starting courier_imap_pop3d_ssl. # /usr/local/etc/rc.d/courier-imap-imapd-ssl.sh start Starting courier_imap_imapd_ssl.
You can't use a regular telnet to test it, because all your communication needs to be encrypted, but openssl has an SSL client you can use to make an encrypted connection for testing:
# openssl s_client -connect localhost:995 # pop3 over ssl, port 995 # openssl s_client -connect localhost:993 # imap over ssl, port 993
See the previous exercise (#6) for the commands to use with each connection.
If you were running the service commercially you might want to consider a certificate signed by a recognised CA, rather than using a self-signed certificate.