In this tutorial i'll show you how you can run postfix on other port than 25. After you've installed postfix edit the /etc/postfix/master.cf file and modify this line:
smtp inet n - n - - smtpd
#smtp inet n - n - - smtpd
10025 inet n - n - - smtpd
After that restart postfix.
This way your postfix daemon will listen to 10025 insted of 25. This is usefull for ISP's that blocks Incoming/Outgoing 25 port. Or you can even run 2 mail daemons on same server ( one from qmail and other from postfix) and deliver mails from one to another. For example Plesk come with qmail, and you hate qmail:).
You can even route mails from qmail to postfix and have postfix deliver the mails:
# cat /var/qmail/control/smtproutes
This way mails that goes out from qmail then to postfix then out of the server.
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