I noticed the postsrsd service is already installed and running in the mtacd docker container. But the feature is not enabled in the main.cf postfix configuration file.
After uncommenting these 2 lines
#sender_canonical_maps = tcp:localhost:10001
#sender_canonical_classes = envelope_sender
and restarting the postsrsd and postfix services, it started rewriting sender addreses.
I have noticed, however, that every email sent from local mailboxes AND email sent to forwarders has its sender rewritten. It would be nice to only rewrite for forwarders though, but I don't know how to accomplish that. (even so, emails appear to be delivered fine).
For the enhance team: Is there a technical, already known issue why this feature is disabled? I re-disabled it for the time being, just in case.
NOTE: I can't assure this works completely fine. If you test it, do it at your own risk.