I'm running Postfix 3.1.0, acting as backup MX (i.e. I have relay_domains set) for a domain whose valid recipients I cannot practically know. Thus, I would normally be producing backscatter when I accept misdirected messages (usually spam that's not spammy enough to get rejected by Rspamd) for the next-hop domain.
I have set bounce_service_name = discard to suppress all bouncing, but this means my own users don't get legitimate bounces.
The only other relevant question I could find here suggested it's impossible to selectively suppress bouncing. Given that six years have passed since then, is that still true?
One possible solution, I thought, would be if the bounce service (in master.cf) can be configured with transport_maps; is that possible?
