apt-get install postfix postfix-mysql mysql-client mysql-server courier-authdaemon courier-authlib-mysql courier-pop courier-pop-ssl courier-imap courier-imap-ssl postfix-tls libsasl2 libsasl2-modules libsasl2-modules-sql sasl2-bin libpam-mysql openssl 

Create directories for web-based administration ? <-- No
General type of configuration? <-- Internet Site
Mail name? <-- server1.example.com
SSL certificate required <-- Ok

mysqladmin -u root password yourrootsqlpassword
mysqladmin -u root -p create mail
mysql -u root -p
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;
USE mail;
CREATE TABLE domains ( domain varchar(50) NOT NULL, PRIMARY KEY (domain) )
TYPE=MyISAM;
CREATE TABLE forwardings ( source varchar(80) NOT NULL, destination TEXT NOT NULL,
PRIMARY KEY (source) )
TYPE=MyISAM;
CREATE TABLE users ( email varchar(80) NOT NULL, password varchar(35) NOT NULL,
PRIMARY KEY (email) ) TYPE=MyISAM;
CREATE TABLE transport ( domain varchar(128) NOT NULL default '',
transport varchar(128) NOT NULL default '', UNIQUE KEY domain (domain)
) TYPE=MyISAM;
quit;

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

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

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

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

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

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

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

postconf -e 'myhostname = server1.example.com'
postconf -e 'mydestination = server1.example.com, localhost, localhost.localdomain'
postconf -e 'mynetworks = 127.0.0.0/8'
postconf -e 'virtual_alias_domains ='
postconf -e 'virtual_alias_maps = proxy:mysql:/etc/postfix/mysql-virtual_forwardings.cf, mysql:/etc/postfix/mysql-virtual_email2email.cf'
postconf -e 'virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql-virtual_domains.cf'
postconf -e 'virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql-virtual_mailboxes.cf'
postconf -e 'virtual_mailbox_base = /home/vmail'
postconf -e 'virtual_uid_maps = static:5000'
postconf -e 'virtual_gid_maps = static:5000'
postconf -e 'smtpd_sasl_auth_enable = yes'
postconf -e 'broken_sasl_auth_clients = yes'
postconf -e 'smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination'
postconf -e 'smtpd_use_tls = yes'
postconf -e 'smtpd_tls_cert_file = /etc/postfix/smtpd.cert'
postconf -e 'smtpd_tls_key_file = /etc/postfix/smtpd.key'
postconf -e 'transport_maps = proxy:mysql:/etc/postfix/mysql-virtual_transports.cf'
postconf -e 'virtual_create_maildirsize = yes'
postconf -e 'virtual_mailbox_extended = yes'
postconf -e 'proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $relay_domains $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $transport_maps $mynetworks'

cd /etc/postfix
openssl req -new -outform PEM -out smtpd.cert -newkey rsa:2048 -nodes -keyout smtpd.key -keyform PEM -days 365 -x509
chmod o= /etc/postfix/smtpd.key

mkdir -p /var/spool/postfix/var/run/saslauthd
nano /etc/default/saslauthd

#
# Settings for saslauthd daemon
#

# Should saslauthd run automatically on startup? (default: no)
START=yes

# Which authentication mechanisms should saslauthd use? (default: pam)
#
# Available options in this Debian package:
# getpwent  -- use the getpwent() library function
# kerberos5 -- use Kerberos 5
# pam       -- use PAM
# rimap     -- use a remote IMAP server
# shadow    -- use the local shadow password file
# sasldb    -- use the local sasldb database file
# ldap      -- use LDAP (configuration is in /etc/saslauthd.conf)
#
# Only one option may be used at a time. See the saslauthd man page
# for more information.
#
# Example: MECHANISMS="pam"
MECHANISMS="pam"

# Additional options for this mechanism. (default: none)
# See the saslauthd man page for information about mech-specific options.
MECH_OPTIONS=""

# How many saslauthd processes should we run? (default: 5)
# A value of 0 will fork a new process for each connection.
THREADS=5

# Other options (default: -c)
# See the saslauthd man page for information about these options.
#
# Example for postfix users: "-c -m /var/spool/postfix/var/run/saslauthd"
# Note: See /usr/share/doc/sasl2-bin/README.Debian
OPTIONS="-c -m /var/spool/postfix/var/run/saslauthd -r"

auth    required   pam_mysql.so user=mail_admin passwd=mail_admin_password
 host=127.0.0.1 db=mail table=users usercolumn=email passwdcolumn=password crypt=1
account sufficient pam_mysql.so user=mail_admin passwd=mail_admin_password
 host=127.0.0.1 db=mail table=users usercolumn=email passwdcolumn=password crypt=1

pwcheck_method: saslauthd
mech_list: plain login
allow_plaintext: true
auxprop_plugin: mysql
sql_hostnames: 127.0.0.1
sql_user: mail_admin
sql_passwd: mail_admin_password
sql_database: mail
sql_select: select password from users where email = '%u'

[...]
authmodulelist="authmysql"
[...]

MYSQL_SERVER localhost
MYSQL_USERNAME mail_admin
MYSQL_PASSWORD mail_admin_password
MYSQL_PORT 0
MYSQL_DATABASE mail
MYSQL_USER_TABLE users
MYSQL_CRYPT_PWFIELD password
#MYSQL_CLEAR_PWFIELD password
MYSQL_UID_FIELD 5000
MYSQL_GID_FIELD 5000
MYSQL_LOGIN_FIELD email
MYSQL_HOME_FIELD "/home/vmail"
MYSQL_MAILDIR_FIELD CONCAT(SUBSTRING_INDEX(email,'@',-1),'/',SUBSTRING_INDEX(email,'@',1),'/')
#MYSQL_NAME_FIELD
MYSQL_QUOTA_FIELD quota

/etc/init.d/courier-authdaemon restart
/etc/init.d/courier-imap restart
/etc/init.d/courier-imap-ssl restart
/etc/init.d/courier-pop restart
/etc/init.d/courier-pop-ssl restart
telnet localhost pop3

server1:/etc/postfix# telnet localhost pop3
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
+OK Hello there.
quit
+OK Better luck next time.
Connection closed by foreign host.

[...]
postmaster: root
root: postmaster@yourdomain.tld
[...]

Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
220 server1.example.com ESMTP Postfix (Debian/GNU)
ehlo localhost
250-server1.example.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH LOGIN PLAIN
250-AUTH=LOGIN PLAIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
quit
221 2.0.0 Bye
Connection closed by foreign host.

mysql -u root -p
USE mail;
INSERT INTO `domains` (`domain`) VALUES ('example.com');
INSERT INTO `users` (`email`, `password`) VALUES ('sales@example.com', VALUES('MD5'));
INSERT INTO `forwardings` (`source`, `destination`) VALUES ('info@example.com','sales@example.com');
INSERT INTO `transport` (`domain`, `transport`) VALUES ('example.com','smtp:mail.example.com');
quit;