daily I'm getting hundreds of these mails and have never been able to quite understand completely. Here are some high level types I have observed for these mails.
From: Mail Delivery Subsystem (firstname.lastname@example.org) Subject: Delivery Status Notification (Delay)
From: Mail Delivery Subsystem (email@example.com) Subject: Delivery Status Notification (Failure)
From: Mail Delivery System (MAILER-DAEMON@www.mydomain.com) Subject: Undelivered Mail Returned to Sender
Question Group 1
What puzzles me is for the DSNs from googlemail.com from Types 1 & 2 above, I'll see 3 mails from it with the following in the body of the mails in sequence over 3 days. 1) Message will be retried for 2 more day(s) 2) Message will be retried for 1 more day(s) 3) Delivery to the following recipient failed permanently
1) If the e-mail address doesn't exist on Google, why doesn't it tell me out right the address is not valid? 2) Assuming that it does exist because Google doesn't say outright on the initial try that it doesn't exist, why it'd still fail on the 3rd day saying "failed permanently"?
Question Group 2
Sometimes I'll be getting e-mails also from googlemail.com but these fall under Type 3 above. Content of the mail will include something like the following:
: host alt1.gmail-smtp-in.l.google.com[18.104.22.168] said: 451 Requested action aborted: local error in processing (in reply to RCPT TO command)
1) Why wouldn't I see Google sending mails under Types 1 & 2 above ultimately telling me "Delivery to the following recipient failed permanently"?
2) What do I do in this case? Is this an invalid address or internal error with Google?
Question Group 3
Sometimes I'll also be getting e-mails with content "mailbox unavailable" from mails under Type 3 above. I'm running Dovecot / Postfix.
How do I make it such that I'll get a list of all the addresses resulted in "mailbox unavailable" so I can batch delete them from my system automatically?