queued mail ... host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user@domain.com> (in reply to end of DATA command)

[Gambix]

I am on PMG 9.12 (fully updated), on enterprise repo.

I have an email that does not get transferred to internal server. I can see in the queue as deferred.

In the deferred tab, it says reason:
host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <USER@DOMAIN.com> (in reply to end of DATA command)

USER@DOMAIN.com is our internal domain that I replaced for privacy. Other mails to same internal domain get in with no issues. This one seems to be stuck.

Please HELP ... SUPPORT?

Michelangelo

 

[Gambix]

It seems to be related to broken mime header. Found a SOLVED thread about this:

A

[SOLVED] Post in thread 'detected undelivered mail to'

Mar 5, 2026

and I updated to PMG9 and the issue is still there for me with Accept Broken MIME Structure enabled

8A9C4181F9C 367715 Thu Mar 5 15:53:23 carla.flores@qsi.ec
(host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <ana@redacted.com> (in reply to end of DATA command))
ana@redacted.com
(host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <info@redacted.com> (in reply to end of DATA command))
info@redacted.com
(host 127.0.0.1[127.0.0.1]...

• andres-asm