Making Postfix Listen to Non Standard Port

Today we found out one of our customers office cannot connect to their mail server, which we host in our data center. They use comcast in their offices and comcast all of a sudden decided to not allow customers use comcast mail server for outgoing mail. Wonderful, no one told us that comcast did that so customer found out the hard way.

Customer configured their outlooks and thunderbirds to point to their mail server on port 25. Alas, nothing works. Our tech support was exhausted from pulling in a near 12 hour shift on some other unrelated non-network tasks. So I decided to investigate this from Bangladesh (as I am in our dev center upgrading our dev network),  I found out that outbound port 25 is blocked by comcast. So I decided to run postfix on a non-standard port (587) by adding the following lines in the /etc/postfix/master.cf:

# Standard port

smtp      inet  n       -       n       -       -       smtpd
# Non-standard port

587       inet  n       -       n       -       -       smtpd

After adding telling postfix to listen to the new non-standard port, I reloaded postix and also told IPTABLES to allow incoming traffic on this port.  Then had the customer’s email client configured to send using the new port and we were back in business!

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