For the record: On Jul 11, 2021, at 1:06 PM, Claus R. Wickinghoff <cl...@mobile.oche.de> wrote:
> I think this can be achieved with reject_unverified_recipient to query > dovecot via lmtp but I've no practical experience with this. Probably you've > to do some googling... That turned out to be the Right Answer. I simply added reject_unverified_recipient to smtpd_recipient_restrictions and that fixed the problem. The chain of events that led to this problem is kind of interesting. What happened was that I migrated my email server from one machine, where it had been running with no problem for many years, to a new machine at a new provider. I had simply copied the main.cf file from the old machine to the new one, but changed the delivery mechanism from direct delivery (i.e. postfix as LDA) to LMTP (i.e. dovecot as LDA). So what was happening before (I think) is that postfix was looking up users in the user DB, not because of smtpd_recipient_restrictions (because I didn’t have that set) but because it had to in order to deliver local messages. When I switched to LMTP that was no longer the case. Postfix now thought it was possible to deliver to non-existent users, and that’s what resulted in the backscatter. Now I understand why the conventional wisdom is not to run your own email server :-) Thanks to all who responded! rg
