apt-get install postfix
apt-get install postfix-mysql
apt-get install apache-suexec
apt-get install courier-maildrop
apt-get install courier-pop
apt-get install courier-imap
apt-get install courier-authlib-mysql
apt-get install courier-authlib
apt-get install sasl2-bin

a2enmod suexec

Important paths:

/etc/courier

/etc/apache2/sites-available/

/etc/postfix

/var/www/extsuite/

/var/mailbox/

SMTP AUTH

/etc/postfix/sasl

saslpasswd2 -c -u mail.159group.hk -a smtpauth 159group