I'm running a PMG 8.2.10 instance that recently seems to have stopped delivering outgoing messages with attachments to at least some recipients. Messages without attachments to the same recipients appear to be delivered successfully. Entries in the tracking centre for outgoing messages with attachments look like below:-
The attachment are well within size limits. I'm far from experienced in postfix, but it seems to me from the above that PMG/postfix is delaying/deferring delivery of said message without making any contact with the recipient mail server? (Happy to be corrected if that's an incorrect assumption). If anyone can point me in the right direction in terms of cause &/or further troubleshooting I'd be grateful.
Code:
2026-03-16T11:34:53.563641+11:00 pmg postfix/smtpd[394818]: connect from mail.mydomain.com.au[10.10.10.5]
2026-03-16T11:34:53.564160+11:00 pmg postfix/smtpd[394818]: 89B7219F56: client=mail.mydomain.com.au[10.10.10.5]
2026-03-16T11:34:53.564944+11:00 pmg postfix/cleanup[394805]: 89B7219F56: message-id=<kcEE.AlCtSDaXSou3H+13JVwROw.gMdns9y03AE@kopano.mydomain.lan>
2026-03-16T11:34:53.578821+11:00 pmg postfix/smtpd[394818]: disconnect from mail.mydomain.com.au[10.10.10.5] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
2026-03-16T11:34:53.579066+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T11:34:53.655668+11:00 pmg postfix/lmtp[394806]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=0.08, delays=0.01/0/0.04/0.03, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T11:41:06.659180+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T11:41:06.750601+11:00 pmg postfix/lmtp[394883]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=373, delays=373/0.01/0.04/0.03, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T11:51:07.881680+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T11:51:07.963485+11:00 pmg postfix/lmtp[394969]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=974, delays=974/0.01/0.04/0.03, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T12:11:07.434674+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T12:11:07.512955+11:00 pmg postfix/lmtp[395153]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=2174, delays=2174/0/0.04/0.03, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T12:51:07.251546+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T12:51:07.398661+11:00 pmg postfix/lmtp[395485]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=4574, delays=4574/0.03/0.04/0.07, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T14:01:07.062065+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T14:01:07.140681+11:00 pmg postfix/lmtp[396105]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=8774, delays=8773/0/0.04/0.02, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T15:11:07.166756+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T15:11:07.250102+11:00 pmg postfix/lmtp[396641]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=12974, delays=12974/0/0.04/0.03, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))
2026-03-16T16:21:07.170817+11:00 pmg postfix/qmgr[321]: 89B7219F56: from=<sender@mydomain.com.au>, size=1302062, nrcpt=1 (queue active)
2026-03-16T16:21:07.244691+11:00 pmg postfix/lmtp[397337]: 89B7219F56: to=<recipient@recipientdomain.com>, relay=127.0.0.1[127.0.0.1]:10023, delay=17174, delays=17174/0.01/0.04/0.02, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <recipient@recipientdomain.com> (in reply to end of DATA command))The attachment are well within size limits. I'm far from experienced in postfix, but it seems to me from the above that PMG/postfix is delaying/deferring delivery of said message without making any contact with the recipient mail server? (Happy to be corrected if that's an incorrect assumption). If anyone can point me in the right direction in terms of cause &/or further troubleshooting I'd be grateful.