Здарова так! И так ! )
Значит вопервых ) гыгыггы
Удаляем стандартный почтовик, смотрите что там у вас стоит сносите бугагаг)
обычно sendmail стоит.
И так ставим CentAlt и epel репозитарии
мой подопотный x64 пример:

rpm -ihv http://centos.alt.ru/repository/centos/6/x86_64/centalt-release-6-1.noarch.rpm
rpm -Uvh http://download.fedora.redhat.com/pub/epel/6/x86_64/epel-release-6-5.noarch.rpm

далее потребуется нам мускуль. там все по простому.

yum install mysql mysql-server mysql-devel mysql-libs php-mysql

стартуйте мускуль

service mysqld start

и настройте чтоб все ровно было 😉

/usr/bin/mysql_secure_installation

сразу перейдем к очень важной байде, это таблица пользователей.
чеб сильно не париться сразу зафигачим ее:

mysql -p
mysql> CREATE DATABASE postfix;
mysql> CREATE USER 'postfix'@'localhost' IDENTIFIED BY 'password';
mysql> GRANT ALL PRIVILEGES ON `postfix`.* TO 'postfix'@'localhost';
mysql> quit;

в полне пойдет.
ставим postfix

yum install postfix

проверьте чеб у нас был мускуля

postconf -m | grep mysql

ok? двигаем дальше
запустим это гамно

chkconfig postfix on
service postfix start

А теперь наберитесь терпения и литр колы.
Будет жарко гыгыгыг ж)
ну очень не просто курить маны и настраивать постфикс фиг знает почему ж)
ладно поехали
фигачи главное гамно /etc/postfix/main.cf
приведу сразу полный конфиг и хватит, чеб мозги не ломать:

soft_bounce = no
queue_directory = /var/spool/postfix
command_directory = /usr/sbin
daemon_directory = /usr/libexec/postfix
data_directory = /var/lib/postfix
mail_owner = postfix
default_privs = nobody
myhostname = mail.сайт.домензона
mydomain = сайт.домензона
myorigin = $mydomain
inet_interfaces = all
inet_protocols = all
mydestination = $myhostname, localhost.$mydomain, localhost
unknown_local_recipient_reject_code = 550
mynetworks = 127.0.0.0/8 ваш айпи сервера
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
smtpd_banner = $myhostname ESMTP
debug_peer_level = 2
debugger_command =
         PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin
         ddd $daemon_directory/$process_name $process_id & sleep 5
sendmail_path = /usr/sbin/sendmail.postfix
newaliases_path = /usr/bin/newaliases.postfix
mailq_path = /usr/bin/mailq.postfix
setgid_group = postdrop
html_directory = no
manpage_directory = /usr/share/man
sample_directory = /usr/share/doc/postfix-2.6.7/samples
readme_directory = /usr/share/doc/postfix-2.6.7/README_FILES
config_directory = /etc/postfix
virtual_mailbox_domains = mysql:$config_directory/sql/vdomains.cf
virtual_mailbox_base = /var/vmail
virtual_mailbox_maps = mysql:$config_directory/sql/vmailbox.cf
virtual_alias_maps = mysql:$config_directory/sql/valias.cf
virtual_minimum_uid = 5000
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1
smtpd_sasl_auth_enable = yes
smtpd_sasl_exceptions_networks = $mynetworks
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination, reject_non_fqdn_recipient, reject_unverified_recipient, reject_rbl_client cbl.abuseat.org

далее стопка конфигаф, все распологаются в /etc/postfix/sql
valias.cf

user = postfix
password = password
hosts = 127.0.0.1
dbname = postfix
table = alias
select_field = goto
where_field = address
additional_conditions = and active = '1'
query = SELECT goto FROM alias WHERE address='%s' AND active = '1'

vdomains.cf

user = postfix
password = password
hosts = 127.0.0.1
dbname = postfix
table = domain
select_field = domain
where_field = domain
additional_conditions = and backupmx = '0' and active = '1'
query = SELECT domain FROM domain WHERE domain='%s' AND backupmx='0' AND active='1'

vmailbox.cf

user = postfix
password = password
hosts = 127.0.0.1
dbname = postfix
table = mailbox
select_field = CONCAT(domain,'/',maildir)
where_field = username
additional_conditions = and active = '1'
query = SELECT CONCAT(domain,'/',maildir) FROM mailbox WHERE username='%s' AND active = '1'

правим /etc/postfix/master.cf

dovecot  unix - n n - - pipe
  flags=DRhu user=vmail:vmail argv=/usr/libexec/dovecot/deliver -d $(recipient)

ставим давкот:

yum -y install dovecot
chkconfig dovecot on

в /etc/dovecot/dovecot.conf фигачим

auth_debug = yes
auth_debug_passwords = yes
auth_mechanisms = plain login
auth_verbose = yes
base_dir = /var/run/dovecot/
first_valid_uid = 5000
last_valid_uid = 5000
log_timestamp = %Y-%m-%d %H:%M:%
mail_gid = mail
mail_location = maildir:/home/vmail/%d/%u
mail_uid = vmail
ssl = no
passdb {
  args = /etc/dovecot/dovecot-sql.conf
  driver = sql
}
protocols = imap pop3
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postdrop
    mode = 0660
    user = postfix
  }
  unix_listener auth-master {
    group = mail
    mode = 0660
    user = vmail
  }
  user = nobody
}
service imap-login {
  executable = /usr/libexec/dovecot/imap-login
  inet_listener imap {
    address = *
    port = 143
  }
}
service imap {
  executable = /usr/libexec/dovecot/imap
}
service pop3-login {
  executable = /usr/libexec/dovecot/pop3-login
  inet_listener pop3 {
    address = *
    port = 110
  }
}
service pop3 {
  executable = /usr/libexec/dovecot/pop3
}

в /etc/dovecot/dovecot-sql.conf

driver = mysql
connect = host=localhost dbname=postfix user=postfix password=password
default_pass_scheme = MD5
user_query = SELECT '/home/vmail/%d/%n' as home, 'maildir:/home/vmail/%d/%n' as mail, 5000 AS uid, 5000 AS gid, concat('dirsize:storage=', quota) AS quota FROM mailbox WHERE username = '%u' AND active = '1'
password_query = SELECT username as user, password, '/home/vmail/%d/%n' as userdb_home, 'maildir:/home/vmail/%d/%n' as userdb_mail, 5000 as userdb_uid, 5000 as userdb_gid FROM mailbox WHERE username = '%u' AND active = '1'

млин запарка ваше)
ставим панельку posfix admin:

wget 'http://sourceforge.net/projects/postfixadmin/files/latest/download'
tar xvf postfixadmin_2.3.4.tar.gz
mv postfixadmin-2.3.4 /var/www/postfix
chown -R apache:apache /var/www/postfix
не забываем прописать в джинсах или апаче )

настраиваем конфиг постфикадмин
var/www/postfix/config.inc.php
и в путь готова!
ps: создадим пользователя группу

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