Before asking my question I should mention that it involves a somewhat dated version of OpenBSD (3.9) and a Microsoft Exchange server. If either of these makes this too off-topic for the list, please accept my apology and ignore this post.
OpenBSD is running sendmail 8.13.4 as a backup MX server for a domain hosted on MS Exchange. (The OpenBSD box has been fantastically reliable in this role, btw. Thanks!). The /etc/mail/aliases file sends root's email to me, in case that's relevant. I receive a fair number of messages from MAILER-DAEMON with the subject "Undeliverable: returned mail: see transcript for details". The messages are always sent to an address I've never heard of, so I assume someone is forging my address in the From: field of their spam. (I've implemented SPF records, incidentally, but it hasn't had a noticeable effect). Here's part of a sample message. Note that mail.mydomain.com is the OpenBSD server: --- BEGIN SAMPLE --- Generating server: mail.mydomain.com [email protected] sitemail.everyone.net #<sitemail.everyone.net #5.1.1 SMTP; 550 Recipient Rejected: No account by that name here> #SMTP# Original message headers: Return-Path: <MAILER-DAEMON> Received: from localhost (localhost) by mail.mydomain.com (8.13.4/8.13.4) id n06HNI36007149; Tue, 6 Jan 2009 09:23:18 -0800 (PST) Date: Tue, 6 Jan 2009 09:23:18 -0800 From: Mail Delivery Subsystem <MAILER-DAEMON> Message-ID: <[email protected]> To: <[email protected]> MIME-Version: 1.0 Content-Type: text/plain Subject: Returned mail: see transcript for details Auto-Submitted: auto-generated (failure) --- END SAMPLE --- This appears straightforward. I was forged as the sender, so I received the bounce. However, here's where I'm confused... The above sample is only the bottom part of what I receive. The top part reads: --- BEGIN SAMPLE --- Delivery has failed to these recipients or distribution lists: [email protected] The recipient's e-mail address was not found in the recipient's e-mail system. Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try resending this message, or provide the following diagnostic text to your system administrator. The following organization rejected your message: mx1.emailsrvr.com. Diagnostic information for administrators: --- END SAMPLE --- What's confusing me is the "Microsoft Exchange will not try to redeliver this message" part. The bottom part says "Generating server: mail.mydomain.com", which is the OpenBSD server. I take that to mean that the OpenBSD machine was trying to deliver the message, not the Exchange server. Plus, the message is from MAILER-DAEMON. Why would [email protected] e-mail me to say that an Exchange server won't retry delivery? It makes sense that the Exchange server is receiving the bounce message for me, (since OpenBSD forwards my mail there), but not that it had anything to do with the original delivery attempt. I must be misunderstanding something about the origin/flow of these messages and would appreciate if anyone can point me in the right direction. Thanks, Richard Koett.
