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 components. In fact it has its own MTA, but we will ignore this (it is still under heavy development, and in my opinion does not have the flexibility needed for an ISP environment). The components we are interested in are the IMAP/POP3 servers and 'sqwebmail', the webmail server.
You can get the entire courier system as one package (including the MTA), or just the components. We will get the pop3/imap and webmail 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.
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.
Start by looking at the port's Makefile:
# cd /usr/ports/mail/courier-authlib # less Makefile
Scan through the Makefile to see the various WITH_XXX options you can select at compilation time. For example, if you want to be able to authenticate against a Mysql database, you can do "make WITH_MYSQL=yes". However, there are only two modules we need - PAM and USERDB - and these are both installed by default. So continue as follows:
# make [If you are prompted for a set of options, hit tab to OK to accept the defaults: namely "PAM support", "authuserdb", and "merge new options"] # make install # make clean (optional step - deletes temporary files in 'work' subdir)
courier-authlib runs a pool of authentication daemons which perform the
actual work; courier-imap and sqwebmail 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.
# cd /usr/local/etc/authlib # vi authdaemonrc change this line: DEBUG_LOGIN=0 to: DEBUG_LOGIN=1
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:
... 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 check your work, especially courier_authdaemond_enable="YES" in /etc/rc.conf
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.
# authtest brian -- find an account called 'brian' # authtest brian foo -- 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:
# cd /usr/ports/mail/courier-imap [Accept default configuration: with OpenSSL and IPv6] # make # make install # make clean (optional step)
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. 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. Escape character is '^]'. * OK Courier-IMAP ready. Copyright 1998-2001 Double Precision, Inc. See COPYING for distribution information. 1 login username password 1 OK LOGIN Ok. 2 examine inbox * FLAGS (\Answered \Flagged \Deleted \Seen \Recent) * OK [PERMANENTFLAGS ()] No permanent flags permitted * 26 EXISTS * 0 RECENT * OK [UIDVALIDITY 989061119] Ok 2 OK [READ-ONLY] Ok 3 logout * BYE Courier-IMAP server shutting down 3 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. 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 following commands will generate certificates for both pop3 and imap services:
# 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
If you were running the service commercially you would be better to get a proper certificate signed by a recognised CA, rather than using a self-signed certificate.
webmail is a very useful service to offer your clients - although you may need to be careful of the extra CPU load and bandwidth it might use.
Unlike many other webmail solutions, which use POP3 or IMAP to talk to the mail store, sqwebmail reads and writes Maildir directories directly. This makes it efficient in the case where POP/IMAP and webmail run on the same box, or where there is an NFS-shared mailstore.
sqwebmail is feature-rich, very customisable through HTML templates and stylesheets, supports multiple languages, and is simple to install (it runs as a single CGI). Note however that it is still under very active development and hence subject to change quite frequently.
If you don't have it, install and test Apache first:
# cd /usr/ports/www/apache13-modssl # make all install clean # vi /etc/rc.conf apache_enable="YES" # /usr/local/etc/rc.d/apache.sh start
Check your Apache install is working by pointing a web browser at http://localhost/
Now install sqwebmail:
# cd /usr/ports/mail/sqwebmail # make WITH_CHARSET=all # make install # make clean (optional step)
The option "WITH_CHARSET=all" allows sqwebmail to view messages in a wide range of character sets. This increases the size of the binary by about one megabyte with the extra translation tables which are included.
Sqwebmail comes in two parts: a small CGI stub which sends HTTP requests
down a socket; and a pool of daemons which perform the actual work. The CGI
stub is installed in /usr/local/www/cgi-bin-dist by default,
and there are some graphics installed in
/usr/local/www/data-dist/sqwebmail/*. These locations will work
for a default Apache install, but if you have changed the normal Apache
configuration (e.g. DocumentRoot) then you may need to copy these somewhere
else.
sqwebmail's main configuration file is
/usr/local/etc/sqwebmail/sqwebmaild - however you almost
certainly don't need to change it.
As usual, you will need to enable the sqwebmail daemon in
/etc/rc.conf, and then call its startup script.
# vi /etc/rc.conf ... sqwebmaild_enable="YES" # /usr/local/etc/rc.d/sqwebmail-sqwebmaild.sh start Starting sqwebmaild.
One other change is required: add the following line to
/etc/crontab to periodically clean out old sessions:
0 * * * * bin /usr/local/share/sqwebmail/cleancache.pl
If everything is working correctly, you should be able to point a web browser at http://localhost/cgi-bin/sqwebmail/sqwebmail and be presented with a login screen, where you can enter a username and password and login.
If this does not work:
/var/log/httpd-access.log and
/var/log/httpd-error.log/var/log/maillog/var/log/debug.logFurther documentation for sqwebmail can be found at
http://www.courier-mta.org/sqwebmail/
and installed in /usr/local/share/doc/sqwebmail/
11.1 Give your neighbour a mail account on your system. Let them check that they can collect mail using POP3, IMAP and Webmail.
11.2 A number of behaviours of courier-imap and sqwebmail can be changed by means of "account options". These can be set globally, and overridden for individual accounts (although not for Unix system accounts). Try the following:
# vi /usr/local/etc/authlib/authdaemonrc change DEFAULTOPTIONS="" to DEFAULTOPTIONS="wbnodsn=1,wbnochangingfrom=1,disableshared=1" # /usr/local/etc/rc.d/courier-authdaemond.sh restart
You can see account options for an account using
"authtest username", and list all accounts together
with their options using "authenumerate -o"
The available options are:
disableshared=1 |
Disable shared folder functionality (hides the 'key' icon in sqwebmail). Shared folders need additional setting up, and only work for systems with virtual accounts. |
disablepop3=1disableimap=1disablewebmail=1 |
Disable these types of access from this account |
wbnochangingfrom=1 |
Webmail: disable ability for users to set the From: header on outgoing mail |
wbnochangepass=1 |
Webmail: disable ability for users to change their passwords |
wbusexsender=1 |
Webmail: add an X-Sender: header to outgoing mail |
wbnoimages=1 |
Webmail: use a text-only interface |
wbnodsn=1 |
Webmail: disable the "return receipt" functionality (Exim does not support this so we must disable it anyway) |
In the simple examples above, we have been using the system password file to authenticate users. When creating new "E-mail only" accounts on your system, you probably don't want your users to be able to login to Unix using ssh or telnet. To disable this, you can simply create their accounts with a nonexistent shell.
# pw useradd username -m -s /nonexistent
To improve security and scalability further, you may wish to keep all your mail accounts in a completely separate password file or database; these users won't be known to Unix at all. The mail directories and messages have to be owned by some Unix user, so we can choose to make them all owned by the 'mailnull' user.
You have many choices of authentication module: for example an LDAP database, a mysql or postgresql database, or a local dbm file (courier supports a format called 'userdb'). These databases will contain the mail login usernames and passwords, and the directories where the mail will be stored. You'll need to configure Courier to use this new database as a login source, and also configure Exim to read this source to determine whether a user exists and where to deliver mail to.
The following example shows how to do this with authuserdb, which is
described in "man makeuserdb" and "man userdb". We'll create two users in
the table, and two empty maildirs. We'll make them under directory
/var/vmail01, which we'll assume is a fast SCSI hard drive. To
support many domains we'll make the POP3 login be user@domain instead
of just a username. We'll have a separate directory for each domain, and
also use the first two characters of the username as subdirectories, so that
if we have ten thousand users for one domain we don't end up with ten
thousand accounts within the same directory.
First we make an empty userdb, and make sure it's not world readable
# touch /usr/local/etc/authlib/userdb # chmod 600 /usr/local/etc/authlib/userdb
Next we create some accounts and empty maildirs:
# userdb fred@flintstone.org set uid=26 gid=6 home=/var/vmail01/flintstone.org/f/r/fred # userdbpw -md5 | userdb fred@flintstone.org set systempw Password: wibble Reenter password: wibble # mkdir -p /var/vmail01/flintstone.org/f/r/fred # maildirmake /var/vmail01/flintstone.org/f/r/fred/Maildir # chown -R mailnull:mail /var/vmail01/flintstone.org/f/r/fred # userdb wilma@flintstone.org set uid=26 gid=6 home=/var/vmail01/flintstone.org/w/i/wilma # userdbpw -md5 | userdb wilma@flintstone.org set systempw Password: boing Reenter password: boing # mkdir -p /var/vmail01/flintstone.org/w/i/wilma # maildirmake /var/vmail01/flintstone.org/w/i/wilma/Maildir # chown -R mailnull:mail /var/vmail01/flintstone.org/w/i/wilma
(In real life you'd write a script to automate this process for creating new accounts). The compulsory fields we need to provide are "home" and numeric "uid" and "gid"; these are documented in "man makeuserdb".
Now we check the userdb contents - it's just a plain text file - then convert it into userdb.dat which is the fast indexed version that authuserdb reads. Note that authuserdb requires encrypted passwords.
# cat /usr/local/etc/authlib/userdb fred@flintstone.org home=/var/vmail01/f/flintstone.org/fred|systempw=$1$96YgsKCe$0oey3dzw0mztdby6ICFxR0|gid=6|uid=26 wilma@flintstone.org home=/var/vmail01/f/flintstone.org/wilma|systempw=$1$nXNJyXcB$1mItZjaFmOV/3YHby8SGu0|gid=6|uid=26 # makeuserdb # ls -l /usr/local/etc/authlib/userdb.dat -rw-r--r-- 1 root wheel 65536 May 14 16:23 /usr/local/etc/authlib/userdb.dat
Now you can configure courier-imap and sqwebmail to login using these new accounts. If you leave authpam in the configuration then you can login with both the userdb accounts and the system accounts. If you removed authuserdb from the list of authentication modules earlier, then put it back now:
# vi /usr/local/etc/authlib/authdaemonrc ... authmodulelist="authuserdb authpam" ... # /usr/local/etc/rc.d/courier-authdaemond.sh stop # /usr/local/etc/rc.d/courier-authdaemond.sh start
At this point you should be able to login using one of the new accounts, and see the (empty) mail directory.
# telnet localhost 110 Trying 127.0.0.1... Connected to localhost.presanog.org.bt. Escape character is '^]'. +OK Hello there. user fred@flintstone.org +OK Password required. pass wibble +OK logged in. stat +OK 0 0 quit +OK Bye-bye. Connection closed by foreign host.
If this doesn't work, follow the instructions for debugging
authentication problems given earlier. Remember the authtest and
authenumerate commands, and look in /var/log/maillog and
/var/log/debug.log
Now all that is necessary is for Exim to know how to deliver messages to
these users. There are a couple of ways this can be done; Exim can be
configured to read /usr/local/etc/authlib/userdb.dat directly, or it can be
configured to talk to courier's authdaemond process. Both can be set up
using Exim's general-purpose configuration language.
It's a tribute to the flexibility of Exim that this can be done even though Exim does not have any specific features for using userdb or authdaemond, although it does mean that the configuration looks complicated at first glance. If you want to find out in detail how these configurations work, you will need to read the Exim documentation carefully.
Firstly, we need a separate list of which domains which need lookups in the userdb database; for simplicitly we will make this a plain text file which is searched linearly. If this gets large it can be converted into an indexed database.
# vi /usr/local/etc/exim/vdomains flintstone.org # vi /usr/local/etc/exim/configure Change the local domains setting to say: domainlist local_domains = @ : lsearch;/usr/local/etc/exim/vdomains
To read /usr/local/etc/authlib/userdb.dat directly, we use the "dbmnz" lookup
type. It's made a bit awkward because courier uses a vertical bar to
separate fields, whereas Exim's "extract" operator expects fields separated
by spaces, but we can use the regular expression substitution operator (sg)
to convert this into the form we want.
[put this immediately after 'begin routers']
userdb:
driver = accept
transport = local_delivery_userdb
domains = lsearch;/usr/local/etc/exim/vdomains
address_data = ${lookup{$local_part@$domain}dbmnz{/usr/local/etc/authlib/userdb.dat}\
{${sg{$value}{([^=]+)=([^|]+)\\|?}{\$1="\$2" }}}fail}
# note the space between "\$2" and }}}
# If the address_data lookup succeeds, then we'll go to the transport.
# But if the address_data lookup fails, then we fall through to here; all
# remaining addresses in vdomains need to be bounced.
userdb_bounce:
driver = redirect
domains = lsearch;/usr/local/etc/exim/vdomains
data = :fail:unknown user
allow_fail
fail_verify
[put this anywhere after 'begin transports']
local_delivery_userdb:
driver = appendfile
directory = ${extract{home}{$address_data}}/${extract{mail}{$address_data}{$value}{Maildir}}/
maildir_format
maildir_use_size_file
delivery_date_add
envelope_to_add
return_path_add
user = ${extract{uid}{$address_data}}
group = ${extract{gid}{$address_data}}
maildir_tag = ,S=$message_size
quota_size_regex = ,S=(\d+)
quota = ${if match{${extract{quota}{$address_data}}}{([0-9]+)S}{$1}{}}
quota_filecount = ${if match{${extract{quota}{$address_data}}}{([0-9]+)C}{$1}{}}
quota_warn_threshold = 90%
Once you've done this, test using
# /usr/local/sbin/exim -bt brian@flintstone.org brian@flintstone.org is undeliverable: unknown user # /usr/local/sbin/exim -bt fred@flintstone.org fred@flintstone.org router = userdb, transport = local_delivery_userdb # /usr/local/sbin/exim -v fred@flintstone.org Subject: test hello . LOG: MAIN <= root@noc.presanog.org.bt U=root P=local S=302 LOG: MAIN => fred <fred@flintstone.org> R=userdb T=local_delivery_userdb LOG: MAIN Completed
It's even possible for Exim to send a request to courier's authdaemond process to perform the lookup, which has the advantage that it will work for any courier authentication module or combination of modules. However there are similar difficulties with parsing the response properly, and the debug output you get from courier is not as good as Exim produces.
[put this immediately after 'begin routers']
# We use manualroute with empty route_data as a dummy router, just to
# set address_data to the value read from the socket.
authdaemon_lookup:
driver = manualroute
route_data =
domains = lsearch;/usr/local/etc/exim/vdomains
address_data = ${sg{${readsocket{/usr/local/var/spool/authdaemon/socket}\
{PRE . exim $local_part@$domain\n}}}{([^=]+)=([^\n]+)\n}{\$1="\$2" }}
# note the space between "\$2" and }}
# Next, if the response contains HOME= then we know this address is valid
# and we can send it to the local delivery transport
courier:
driver = accept
transport = local_delivery_courier
domains = lsearch;/usr/local/etc/exim/vdomains
condition = ${extract{HOME}{$address_data}{1}{0}}
# Otherwise, the address was bad. If it contains FAIL then it's a permanant
# failure, otherwise it's a temporary failure
courier_bounce:
driver = redirect
domains = lsearch;/usr/local/etc/exim/vdomains
data = ${if match{$address_data}{FAIL}{:fail:unknown user}fail}
allow_fail
fail_verify
[transports]
local_delivery_courier:
driver = appendfile
directory = ${extract{HOME}{$address_data}}/${extract{MAILDIR}{$address_data}{$value}{Maildir}}/
maildir_format
maildir_use_size_file
delivery_date_add
envelope_to_add
return_path_add
user = ${extract{UID}{$address_data}}
group = ${extract{GID}{$address_data}}
maildir_tag = ,S=$message_size
quota_size_regex = ,S=(\d+)
quota = ${if match{${extract{QUOTA}{$address_data}}}{([0-9]+)S}{$1}{}}
quota_filecount = ${if match{${extract{QUOTA}{$address_data}}}{([0-9]+)C}{$1}{}}
quota_warn_threshold = 90%
Finally, if you are building a box where you know that all the mail will be owned by the 'exim' or 'mailnull' user, then in fact the daemons no longer need to run with root privileges - they can run as the exim user only, as they never have to change to any other userid. This in theory should make your system more secure.
There are some steps you can take to do this for each daemon:
/usr/local/etc/exim/configure. You'll probably also have
to adjust permissions so that the exim user has access to the authdaemon
socket:
# chown mailnull:mail /usr/local/var/spool/authdaemon
... TCPDOPTS="-nodnslookup -noidentlookup -user=mailnull" ...
# su mailnull -c "/usr/local/etc/rc.d/sqwebmail-sqwebmaild.sh start"However, for this to work, you first need to sort out some permissions issues: you need to recompile and reinstall sqwebmail using
# make WITH_CACHEOWNER=mailnulland change the entry in /etc/crontab to run cleancache.pl as user 'mailnull' not user 'bin'. You also need to change ownerships of the configuration files and temporary directory:
# cd /usr/local/etc # chown mailnull:mail sqwebmail/sqwebmaild authlib/authdaemonrc # chown -R mailnull:mail /usr/local/var/sqwebmail