Virtual Users And Domains With Postfix, Courier, MySQL And SquirrelMail (Ubuntu 13.10)

This tutorial is Copyright (c) 2014 by Falko Timme & Srijan Kishore. It is derived from a tutorial from Christoph Haas which you can find at http://workaround.org. You are free to use this tutorial under the Creative Commons license 2.5 or any later version.

This document describes how to install a Postfix mail server that is based on virtual users and domains, i.e. users and domains that are in a MySQL database. I'll also demonstrate the installation and configuration of Courier (Courier-POP3, Courier-IMAP), so that Courier can authenticate against the same MySQL database Postfix uses.

The resulting Postfix server is capable of SMTP-AUTH and TLS and quota (quota is not built into Postfix by default, I'll show how to patch your Postfix appropriately). Passwords are stored in encrypted form in the database (most documents I found were dealing with plain text passwords which is a security risk). In addition to that, this tutorial covers the installation of Amavisd, SpamAssassin and ClamAV so that emails will be scanned for spam and viruses. I will also show how to install SquirrelMail as a webmail interface so that users can read and send emails and change their passwords.

The advantage of such a "virtual" setup (virtual users and domains in a MySQL database) is that it is far more performant than a setup that is based on "real" system users. With this virtual setup your mail server can handle thousands of domains and users. Besides, it is easier to administrate because you only have to deal with the MySQL database when you add new users/domains or edit existing ones. No more postmap commands to create db files, no more reloading of Postfix, etc. For the administration of the MySQL database you can use web based tools like phpMyAdmin which will also be installed in this howto. The third advantage is that users have an email address as user name (instead of a user name + an email address) which is easier to understand and keep in mind.

This howto is meant as a practical guide; it does not cover the theoretical backgrounds. They are treated in a lot of other documents in the web.

This document comes without warranty of any kind! I want to say that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!

1 Preliminary Note

This tutorial is based on Ubuntu 13.10 Server (Saucy Salamander), so you should set up a basic Ubuntu 13.10 server installation before you continue with this tutorial. The system should have a static IP address. I use 192.168.0.100 as my IP address in this tutorial and server1.example.com as the hostname.

Make sure that you are logged in as root (type in

sudo su

to become root), because we must run all the steps from this tutorial as root user.

It is very important that you make /bin/sh a symlink to /bin/bash...

dpkg-reconfigure dash

Use dash as the default system shell (/bin/sh)? <-- No

... and that you disable AppArmor:

/etc/init.d/apparmor stop 
update-rc.d -f apparmor remove 
apt-get remove apparmor apparmor-utils

2 Install Postfix, Courier, Saslauthd, MySQL, phpMyAdmin

To install Postfix, Courier, Saslauthd, MySQL, and phpMyAdmin, we simply run

apt-get install postfix postfix-mysql postfix-doc mysql-client mysql-server courier-authdaemon courier-authlib-mysql courier-pop courier-pop-ssl courier-imap courier-imap-ssl libsasl2-2 libsasl2-modules libsasl2-modules-sql sasl2-bin libpam-mysql openssl phpmyadmin apache2 libapache2-mod-php5 php5 php5-mysql libpam-smbpass

You will be asked a few questions:

New password for the MySQL "root" user: <-- yourrootsqlpassword
Repeat password for the MySQL "root" user: <-- yourrootsqlpassword
Create directories for web-based administration? <-- No
General type of mail configuration: <-- Internet Site
System mail name: <-- server1.example.com
SSL certificate required <-- Ok
Web server to reconfigure automatically: <-- apache2
Configure database for phpmyadmin with dbconfig-common? <-- No

3 Apply The Quota Patch To Postfix

We have to get the Postfix sources, patch it with the quota patch, build new Postfix .deb packages and install those .deb packages:

apt-get build-dep postfix

cd /usr/src
apt-get source postfix

(Make sure you use the correct Postfix version in the following commands. I have Postfix 2.10.2 installed. You can find out your Postfix version by running

postconf -d | grep mail_version

The output should look like this:

root@server1:/usr/src# postconf -d | grep mail_version
mail_version = 2.10.2
milter_macro_v = $mail_name $mail_version
root@server1:/usr/src#

wget http://vda.sourceforge.net/VDA/postfix-vda-v13-2.10.0.patch
cd postfix-2.10.2
patch -p1 < ../postfix-vda-v13-2.10.0.patch

Next open debian/rules and change DEB_BUILD_HARDENING from 1 to 0:

vi debian/rules

[...]
export DEB_BUILD_HARDENING=0
[...]

If you don't do this, your build will fail with the following error messages:

maildir.c: In function âdeliver_maildirâ:
maildir.c:974:17: error: format not a string literal and no format arguments [-Werror=format-security]
maildir.c:977:17: error: format not a string literal and no format arguments [-Werror=format-security]
maildir.c:983:17: error: format not a string literal and no format arguments [-Werror=format-security]
maildir.c:986:17: error: format not a string literal and no format arguments [-Werror=format-security]
maildir.c: In function âsql2fileâ:
maildir.c:404:25: warning: ignoring return value of âreadâ, declared with attribute warn_unused_result [-Wunused-result]
maildir.c:417:26: warning: ignoring return value of âwriteâ, declared with attribute warn_unused_result [-Wunused-result]
cc1: some warnings being treated as errors
make: *** [maildir.o] Error 1
make: Leaving directory `/usr/src/postfix-2.10.2/src/virtual'
make[1]: *** [update] Error 1
make[1]: Leaving directory `/usr/src/postfix-2.10.2'
make: *** [build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
root@server1:/usr/src/postfix-2.10.2#

Now we can build the new Postfix .deb packages:

dpkg-buildpackage

Now we go one directory up, that's where the new .deb packages have been created:

cd ..

The command

ls -l

shows you the available packages:

root@server1:/usr/src# ls -l
total 7124
drwxr-xr-x 18 root root    4096 Apr 16 04:29 postfix-2.10.2
-rw-r--r--  1 root root   48594 Apr 16 04:29 postfix-cdb_2.10.2-1_amd64.deb
-rw-r--r--  1 root root  161974 Apr 16 04:29 postfix-dev_2.10.2-1_all.deb
-rw-r--r--  1 root root 1094344 Apr 16 04:29 postfix-doc_2.10.2-1_all.deb
-rw-r--r--  1 root root   57342 Apr 16 04:29 postfix-ldap_2.10.2-1_amd64.deb
-rw-r--r--  1 root root   50554 Apr 16 04:29 postfix-mysql_2.10.2-1_amd64.deb
-rw-r--r--  1 root root   50804 Apr 16 04:29 postfix-pcre_2.10.2-1_amd64.deb
-rw-r--r--  1 root root   50756 Apr 16 04:29 postfix-pgsql_2.10.2-1_amd64.deb
-rw-r--r--  1 root root   55701 Jun  7  2013 postfix-vda-v13-2.10.0.patch
-rw-r--r--  1 root root  282175 Apr 16 04:28 postfix_2.10.2-1.diff.gz
-rw-r--r--  1 root root    1522 Apr 16 04:28 postfix_2.10.2-1.dsc
-rw-r--r--  1 root root    3899 Apr 16 04:29 postfix_2.10.2-1_amd64.changes
-rw-r--r--  1 root root 1542368 Apr 16 04:29 postfix_2.10.2-1_amd64.deb
-rw-r--r--  1 root root 3828326 Sep 12  2013 postfix_2.10.2.orig.tar.gz

Pick the postfix and postfix-mysql packages and install them like this:

dpkg -i postfix_2.10.2-1_amd64.deb postfix-mysql_2.10.2-1_amd64.deb

4 Create The MySQL Database For Postfix/Courier

Now we create a database called mail:

mysqladmin -u root -p create mail

You will be asked for this question:

Enter Password: <-- yourrootsqlpassword

Next, we go to the MySQL shell:

mysql -u root -p

On the MySQL shell, we create the user mail_admin with the passwort mail_admin_password (replace it with your own password) who has SELECT,INSERT,UPDATE,DELETE privileges on the mail database. This user will be used by Postfix and Courier to connect to the mail database:

GRANT SELECT, INSERT, UPDATE, DELETE ON mail.* TO 'mail_admin'@'localhost' IDENTIFIED BY 'mail_admin_password';
GRANT SELECT, INSERT, UPDATE, DELETE ON mail.* TO 'mail_admin'@'localhost.localdomain' IDENTIFIED BY 'mail_admin_password';
FLUSH PRIVILEGES;

Still on the MySQL shell, we create the tables needed by Postfix and Courier:

USE mail;

CREATE TABLE domains (
domain varchar(50) NOT NULL,
PRIMARY KEY (domain) )
ENGINE=MyISAM;

CREATE TABLE forwardings (
source varchar(80) NOT NULL,
destination TEXT NOT NULL,
PRIMARY KEY (source) )
ENGINE=MyISAM;

CREATE TABLE users (
email varchar(80) NOT NULL,
password varchar(20) NOT NULL,
quota INT(10) DEFAULT '10485760',
PRIMARY KEY (email)
) ENGINE=MyISAM;

CREATE TABLE transport (
domain varchar(128) NOT NULL default '',
transport varchar(128) NOT NULL default '',
UNIQUE KEY domain (domain)
) ENGINE=MyISAM;

quit;

As you may have noticed, with the quit; command we have left the MySQL shell and are back on the Linux shell.

The domains table will store each virtual domain that Postfix should receive emails for (e.g. example.com).

The forwardings table is for aliasing one email address to another, e.g. forward emails for [email protected] to [email protected].

The users table stores all virtual users (i.e. email addresses, because the email address and user name is the same) and passwords (in encrypted form!) and a quota value for each mail box (in this example the default value is 10485760 bytes which means 10MB).

The transport table is optional, it is for advanced users. It allows to forward mails for single users, whole domains or all mails to another server. For example,

would forward all emails for example.com via the smtp protocol to the server with the IP address 1.2.3.4 (the square brackets [] mean "do not make a lookup of the MX DNS record" (which makes sense for IP addresses...). If you use a fully qualified domain name (FQDN) instead you would not use the square brackets.).

BTW, (I'm assuming that the IP address of your mail server system is 192.168.0.100) you can access phpMyAdmin over http://192.168.0.100/phpmyadmin/ in a browser and log in as mail_admin. Then you can have a look at the database. Later on you can use phpMyAdmin to administrate your mail server.

5 Configure Postfix

Now we have to tell Postfix where it can find all the information in the database. Therefore we have to create six text files. You will notice that I tell Postfix to connect to MySQL on the IP address 127.0.0.1 instead of localhost. This is because Postfix is running in a chroot jail and does not have access to the MySQL socket which it would try to connect if I told Postfix to use localhost. If I use 127.0.0.1 Postfix uses TCP networking to connect to MySQL which is no problem even in a chroot jail (the alternative would be to move the MySQL socket into the chroot jail which causes some other problems).

Please make sure that /etc/mysql/my.cnf contains the following line:

vi /etc/mysql/my.cnf

[...]
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address           = 127.0.0.1
[...]

If you had to modify /etc/mysql/my.cnf, please restart MySQL now:

/etc/init.d/mysql restart

Run

netstat -tap | grep mysql

to make sure that MySQL is listening on 127.0.0.1 (localhost.localdomain):

root@server1:~# netstat -tap | grep mysql
tcp        0      0 localhost.localdo:mysql *:*                     LISTEN      24970/mysqld    
root@server1:~#

Now let's create our six text files.

vi /etc/postfix/mysql-virtual_domains.cf

user = mail_admin
password = mail_admin_password
dbname = mail
query = SELECT domain AS virtual FROM domains WHERE domain='%s'
hosts = 127.0.0.1

vi /etc/postfix/mysql-virtual_forwardings.cf

user = mail_admin
password = mail_admin_password
dbname = mail
query = SELECT destination FROM forwardings WHERE source='%s'
hosts = 127.0.0.1

vi /etc/postfix/mysql-virtual_mailboxes.cf

user = mail_admin
password = mail_admin_password
dbname = mail
query = SELECT CONCAT(SUBSTRING_INDEX(email,'@',-1),'/',SUBSTRING_INDEX(email,'@',1),'/') FROM users WHERE email='%s'
hosts = 127.0.0.1

vi /etc/postfix/mysql-virtual_email2email.cf

user = mail_admin
password = mail_admin_password
dbname = mail
query = SELECT email FROM users WHERE email='%s'
hosts = 127.0.0.1

vi /etc/postfix/mysql-virtual_transports.cf

user = mail_admin
password = mail_admin_password
dbname = mail
query = SELECT transport FROM transport WHERE domain='%s'
hosts = 127.0.0.1

vi /etc/postfix/mysql-virtual_mailbox_limit_maps.cf

user = mail_admin
password = mail_admin_password
dbname = mail
query = SELECT quota FROM users WHERE email='%s'
hosts = 127.0.0.1

Then change the permissions and the group of these files:

chmod o= /etc/postfix/mysql-virtual_*.cf
chgrp postfix /etc/postfix/mysql-virtual_*.cf

Now we create a user and group called vmail with the home directory /home/vmail. This is where all mail boxes will be stored.

groupadd -g 5000 vmail
useradd -g vmail -u 5000 vmail -d /home/vmail -m

Next we do some Postfix configuration. Go sure that you replace server1.example.com with a valid FQDN, otherwise your Postfix might not work properly!

postconf -e 'myhostname = server1.example.com'
postconf -e 'mydestination = server1.example.com, localhost, localhost.localdomain'
postc