We run an Ubuntu server with Webmin + Virtualmin and some of our virtual servers have their own dedicated ip. I configured Postfix to use the right IP address dependent on the sender domain, and it works but we see some of our email if being rejected by spam filters due to the HELO Postfix is using.
By default, Postfix seems to use $myhostname in the HELO header so it is using the server's fqdn for all domains, regardless they use their own ip address or not. Some spam filters require the HELO header to match the rDNS of the sender IP. I tried adding "-o myhostname=example.com" in master.cf, like this:
smtp-149191093214570 unix - - y - - smtp -o smtp_bind_address=188.8.131.52 -o myhostname=example.com
This way, Postfix send the right HELO, but manually maintaining the master.cf file is not an option. Is there a way to add that parameter to master.cf with webmin/virtualmin?