[tor-bugs] #30911 [Internal Services/Tor Sysadmin Team]: sending email to unknown recipient @tpo gets transient error instead of permanent?

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#30911: sending email to unknown recipient @tpo gets transient error instead of
permanent?
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 Reporter:  catalyst                             |          Owner:  anarcat
     Type:  defect                               |         Status:
                                                 |  assigned
 Priority:  Medium                               |      Milestone:
Component:  Internal Services/Tor Sysadmin Team  |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:                                       |  Actual Points:
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by anarcat):

 First off, I want to confirm that I have also suffered the same fate:
 you're not alone! :) I found it weird that my mail didn't get through
 first, then realized my mistake when looking at the headers, then wondered
 why the message didn't bounce, then resent the message, and *then*
 received the bounce, a week later. It's rather strange. ;)

 I think I found out why this happens. In the Postfix server, we use the
 [http://www.postfix.org/postconf.5.html#reject_unverified_recipient
 reject_unverified_recipient]
 [http://www.postfix.org/postconf.5.html#smtpd_recipient_restrictions
 smtpd_recipient_restrictions], which, by default, will fail with a
 temporary error code (450) at first, which means it will stay in the queue
 for 7 days.

 I believe there are two possible fixes for this problem:

 1. add [http://www.postfix.org/postconf.5.html#reject_unlisted_recipient
 reject_unlisted_recipient] to the list of restrictions, which will
 immediately refuse emails with an unknown recipient, on submission,
 without queuing it

 2. change the
 [http://www.postfix.org/postconf.5.html#unverified_recipient_reject_code
 unverified_recipient_reject_code] to 550, but that says: "Do not change
 this unless you have a complete understanding of
 [https://tools.ietf.org/html/rfc5321 RFC 5321]." ... which I'm not sure
 *anyone* can truly claim to have.

 I'm running with the former at home. I'll check with my colleagues to
 validate the former is the right approach and we should be able to deploy
 this fix shortly. I won't do that today, unfortunately, because it's the
 weekend and I want to have tomorrow off. ;) But soon next week, hopefully.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/30911#comment:2>
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