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))