On Tue, Jan 06, 2026 at 02:32:10PM +0100, Sidney Cadot wrote: > What happens, apparently, is that the message dropoff is rejected with a > "550 Invalid recipient" response.
Because the local user it would be delivered to does not exist. The fact that you are doing your own custom processing of the message using a script which doesn't actually deliver the mail anywhere doesn't alter the fact that smtpd wants to 'deliver' it to a valid user. > Now I have read the "smtpd.conf" man page a few times, but I don't see an > explanation about why the message is rejected. It's not explicitly mentioned in the smtpd manual pages, but in general 'mda' is a term for a program that does _local delivery_, so the name basically imples that you can't use it as a general mail handling mechanism. > My questions: > > * Is this behavior expected, and if so, is it documented? Expected, yes. Documented, yes and no, it's probably obvious for anyone with experience of smtp based mail systems, less so for newcomers. > * What should I change in my smtpd.conf to get incoming messages accepted > into the mail queue? > > As soon as that works, I can direct my attention to the following steps -- > altering the deliver-to of the messages, and relaying them to my ISPs SMTP > server. I probably will have some questions about that too. But first I > need to make sure messages are queued. Honestly, although I understand your thinking for wanting to learn how smtpd works, you are probably doing this the hard way. Just set up a simple, normal mail delivery configuration, and get that working first. Then look inside it using logs, debug options, and then maybe some custom scripts to do non-standard things with received mail.
