bounce-detection fails for hotmail 'User unknown in virtual mailbox table'

The DSN is not compliant with RFC 3464 <http://www.rfc-editor.org/rfc/rfc3464.txt>.

The DSN contains in it's message/delivery-status part

Reporting-MTA: dns; mx1.maillist.peak.org
Received-From-MTA: dns;
Arrival-Date: Wed, 9 Sep 2009 17:37:13 -0700
Final-Recipient: rfc822; <email address hidden>
X-Actual-Recipient: rfc822; <email address hidden>

Action: failed
Status: 5.1.1
Last-Attempt-Date: Wed, 9 Sep 2009 17:37:13 -0700
Diagnostic-Code: smtp;
 550 <email address hidden>: User unknown in virtual mailbox
 table

The empty line is supposed to separate the per message fields from the per recipient fields. I.e., the contents of the part should be

Reporting-MTA: dns; mx1.maillist.peak.org
Received-From-MTA: dns;
Arrival-Date: Wed, 9 Sep 2009 17:37:13 -0700

Final-Recipient: rfc822; <email address hidden>
X-Actual-Recipient: rfc822; <email address hidden>
Action: failed
Status: 5.1.1
Last-Attempt-Date: Wed, 9 Sep 2009 17:37:13 -0700
Diagnostic-Code: smtp;
 550 <email address hidden>: User unknown in virtual mailbox
 table

We only look at the block containing "Action: failed" and since that block in your message doesn't contain any recipient address, we don't find the address.

Note that this DSN seems very strange even disregarding the problem above. It was generated by your own MTA mx1.maillist.peak.org, yet the error "User unknown in virtual mailbox table" indicates one of two things. Either the error was generated from it's own virtual mailbox delivery attempt which says it is trying to deliver this hotmail.com mail to a local virtual mailbox, or the error was received during SMTP with a hotmail.com MX. The former would indicate some serious problem with your MTA configuration, and the latter seems highly unlikely as the particular response is not one typically returned by hotmail.com MXs.

OK. I presume this was an aberration, based on your comment. If it shows up again (would be in about two weeks: The traffic is very low on this list), I'll update this bug.