On 2009-09-27 Erick Calder wrote: > On Sep 27, 2009, at 1:03 PM, LuKreme wrote: >> On Sep 27, 2009, at 2:52 AM, Erick Calder wrote: >>> On Sep 27, 2009, at 12:53 AM, LuKreme wrote: >>>> On Sep 27, 2009, at 0:53, Erick Calder <e...@arix.com> wrote: >>>>> if the message were for no-ex...@arix.com then it gets rerouted >>>>> to n...@arix.com which also doesn't exist and therefor bounces. >>>> >>>> Yes, it bounces. This makes you a backacatter source. This is bad. >>> >>> but doesn't my postfix server bounce by default when receiving a mail >>> for an inexistent address? and if it doesn't, how are users who >>> misspell my address to know their message didn't get delivered? >> >> No, not generally. Unknown users are REJECTed, not bounced. > > ok, I'm not getting this. your statements of 12:53AM and of 1:03PM > seem contradictory... if an address doesn't exist, does it get bounced > (as stated on 12:53AM) or rejected (as stated on 1:03PM, in which case > I'm _not_ a backscatter source, and with which Ansgar and mouss seem > to agree)?
You're just misunderstanding how virtual alias maps work. During the SMTP dialog Postfix checks its various recipient/relay maps for valid recipients. If a valid match is found, the mail is accepted and queued for further relaying. However, Postfix does not expand the virtual alias maps at this point. If you have a match on the left side of your virtual aliases, Postfix does not check whether the corresponding right side entry actually is valid. Basically the process goes like this: - Sending MTA starts SMTP dialog, giving no-ex...@arix.com as the RCPT TO address - Postfix finds mapping no-ex...@arix.com -> n...@arix.com in its virtual alias maps - Postfix accepts the mail and queues it for further delivery, because a valid mapping exists - Next Postfix tries to relay the already accepted mail to n...@arix.com, which is rejected, becaus n...@arix.com doesn't exist - Postfix thus finds itself unable to deliver the mail accepted for no-ex...@arix.com, and thus (as per RFC 2821) MUST generate a bounce That's why you want to accept mail only for valid addresses. Regards Ansgar Wiechers -- "Abstractions save us time working, but they don't save us time learning." --Joel Spolsky
