Hi, I don’t know if you found a solution, but I was having similar problems with a domain that was giving me the error “Sender address rejected: Domain not found”. After much searching and testing I got it to work as follows:
In master.cf add into the option smtpd_sender_restrictions regexp:/opt/postfix/conf/sender_whitelist… in my case it looked like this:
And the sender_whitelist file looks like this:
That’s it, obviously you should run
postmap -v sender_whitelist and
docker compose restart postfix-mailcow to apply the changes.