Ian Eiloart wrote:
Their advice is plain: "Reject, Don't Bounce The standards provide for a mail server to 'reject' a message by refusing its transfer, rather than accepting it and risking future problems."
Although this thread long ago went somewhat off topic for Mailman, I think it's valuable, and there's been a lot of good information here, but I still have a question that I would like information on.
I 'get it' that non-acceptance at SMTP time is good and accepting and bouncing is bad. This was not news to me, I've known it for some time, but here's my situation. I run a server that supports a few domains. By far, the bulk of the mail is Mailman and other mail associated with my cycling club. There are several generic forwarding addresses such as 'president', 'vicepresident', 'board', 'membership', etc. in the club's domain. These are aliased to the appropriate current recipients. Of course, all these recipient addresses are valid and deliverable.
Any mail I receive for an unknown recipient is rejected at SMTP time, the rest is greylisted and a lot of that never returns. That which passes greylisting is run through MailScanner/ClamAV/SpamAssassin, and sometimes discarded or quarrantined, but nothing is ever returned to the sender. So far, so good.
Here's the problem. I receive a message for board@example.net which is aliased to a few other addresses including user@example.com. The MTA (Postfix in my case) accepts the message to board and resends it to the aliased recipients. example.com has a very agressive content filter which rejects messages after receiving the DATA. so Postfix's delivery to user@example.com is sometimes not accepted by example.com so Postfix returns a DSN. Sometimes the sender was legitimate, sometimes (probably more often) not.
So what do I do practically in this case. Calling out to verify the recipient won't help because the recipient is valid. I can arrange for the DSN to pass through MailScanner on the way out and possibly create rules to conditionally drop it, but what should the rules be, and is it really a problem at all? Note for example, that yesterday I did not accept 29985 messages for unknown users and greylisted 5684 more and sent no DSNs. This is somewhat typical except I probably average 2 or 3 DSNs per day. Should I be worried?
-- Mark Sapiro <mark@msapiro.net> The highway is for gamblers, San Francisco Bay Area, California better use your sense - B. Dylan