How to configure mail server forwarding on Postfix – Email forwarding from one Postfix SMTP to another

I needed to configure mail forwarding from one Postfix mail server with a correct MX and PTR record to another one for a reason the second mail server has filtered port 25, because of ISP policy. As it is recommended in such situations, I've configured mail forwarding from postfix host1 to host2 to use (submission) port number 587 which general purpose is for exactly situations like this. Mail forwarding is done via a simple /etc/postfix/main.cf, /usr/local/etc/postfix/main.cf (depending where Postfix is installed).

Thus as my postfix configs are in /etc/postfix, I edited /etc/postfix/main.cf on forwarding Postfix mail server, where mail comes in (host1) and added line:

relayhost = [123.123.123.123]:587

Where 123.123.123.123 is IP address of host2

To load settings I had to do the usual postfix restart

postfix# /etc/rc.d/postfix restart

postfix/postfix-script: stopping the Postfix mail system
postfix/postfix-script: starting the Postfix mail system

On host2 – to which mail is forwarded, I had to add access for host1 to relay mail  in /etc/postfix/main.cf had to include:

mynetworks = 124.124.124.124

and 124.124.124.124 is IP of host1

One note to make is if mynetworks is not defined to host of host1 mail server, you will get in /var/log/maillog error:

Relay access denied (in reply to RCPT TO command))

Here is paste chunk from /var/log/maillog

Mar  1 08:57:01 host1 postfix/smtp[95236]: 88C8B11F911:
                    to=<amaderit.for.brother+caf_=amaderit2013FINAL=forward-host.org@gmail.com>, relay=24.129.36.212[24.129.36.212]:587, delay=0.54,
                    delays=0.01/0/0.44/0.09, dsn=5.7.1, status=bounced (host 24.129.36.212[24.129.36.212] said: 554 5.7.1
                    <amaderit.for.brother+caf_=amaderit2013FINAL=forward-host.org@gmail.com>: Relay access denied (in reply to RCPT TO command))

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3 Responses to “How to configure mail server forwarding on Postfix – Email forwarding from one Postfix SMTP to another”

  1. Fidel Cevallos says:

    Do you mind if I quote a couple of your posts as long as I provide credit and sources back to your site? My blog is in the very same niche as yours and my users would truly benefit from some of the information you provide here. Please let me know if this alright with you. Appreciate it!

  2. James T says:

    This was the missing piece! I've been working on this relay for 3 days using various other forums. Not one has mentioned adding host1's network to host2's main.cf file. Well done.

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