I'm having trouble with two domains that send messages to my users.
The messages are stuck in the postfix queue with the following message:
D76C12740B 178921 Tue Feb 3 19:22:31 msprvs1=20494iL6NYVzL=bounces-321255@domain.com
(host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user@domain.com.br> (in reply to end of DATA command))
user@domain.com.br
DC07D26A55 84919 Tue Feb 3 11:12:29 0100019c23d8f34b-c9c6d85a-eb76-4aa4-abfa-2780936b3aa0-000000@ses.domain.com.br
(host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user2@domain.com.br> (in reply to end of DATA command))
user2@domain.com.br
When I force the queue with `postqueue -f`, the following appears in mail.log.
2026-02-04T15:23:15.280271-03:00 pmg4 postfix/lmtp[183192]: D76C12740B: to=<user@domain.com.br>, relay=127.0.0.1[127.0.0.1]:10024, delay=72044, delays=72026/3.8/14/0.02, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user@domain.com.br> (in reply to end of DATA command))
2026-02-04T15:23:18.413163-03:00 pmg4 pmg-smtp-filter[183254]: 2026/02/04-15:23:18 CONNECT TCP Peer: "[127.0.0.1]:44370" Local: "[127.0.0.1]:10024"
2026-02-04T15:23:18.471585-03:00 pmg4 pmg-smtp-filter[183254]: 2238269838E966F601: message has ambiguous content: ERROR
2026-02-04T15:23:18.472176-03:00 pmg4 pmg-smtp-filter[183254]: fast exit because of errors (free 288780288 bytes)
2026-02-04T15:23:18.474580-03:00 pmg4 postfix/lmtp[183209]: DC07D26A55: to=<user2@domain.com.br>, relay=127.0.0.1[127.0.0.1]:10024, delay=101449, delays=101428/3.8/18/0.02, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user2@domain.com.br> (in reply to end of DATA command))
2026-02-04T15:23:18.722638-03:00 pmg4 pmg-smtp-filter[183256]: 2026/02/04-15:23:18 CONNECT TCP Peer: "[127.0.0.1]:44378" Local: "[127.0.0.1]:10024"
2026-02-04T15:23:18.787487-03:00 pmg4 pmg-smtp-filter[183256]: 2238369838E96BAC1B: unable to parse message - part did not end with expected boundary
2026-02-04T15:23:18.788134-03:00 pmg4 pmg-smtp-filter[183256]: fast exit because of errors (free 288780288 bytes)
pmgversion -v
proxmox-mailgateway: 9.0.0 (API: 9.0.4/f3ea3fa12b03, running kernel: 6.17.4-2-pve)
pmg-api: 9.0.4
pmg-gui: 5.0.4
proxmox-kernel-helper: 9.0.4
proxmox-kernel-6.17.4-2-pve-signed: 6.17.4-2
proxmox-kernel-6.17: 6.17.4-2
proxmox-kernel-6.17.2-2-pve-signed: 6.17.2-2
proxmox-kernel-6.14.11-5-pve-signed: 6.14.11-5
proxmox-kernel-6.14: 6.14.11-5
clamav-daemon: 1.4.3+dfsg-1
ifupdown2: 3.3.0-1+pmx11
libarchive-perl: 3.7.4.1
libjs-extjs: 7.0.0-5
libproxmox-acme-perl: 1.7.0
libproxmox-acme-plugins: 1.7.0
libpve-apiclient-perl: 3.4.2
libpve-common-perl: 9.1.7
libpve-http-server-perl: 6.0.5
libxdgmime-perl: 1.2.0
lvm2: 2.03.31-2+pmx1
pmg-docs: 9.0.5
pmg-i18n: 3.6.6
pmg-log-tracker: 3.0.1
proxmox-mini-journalreader: 1.6
proxmox-spamassassin: 4.0.2-1
proxmox-widget-toolkit: 5.1.5
pve-firmware: 3.17-2
pve-xtermjs: 5.5.0-3
zfsutils-linux: 2.3.4-pve1
The messages are stuck in the postfix queue with the following message:
D76C12740B 178921 Tue Feb 3 19:22:31 msprvs1=20494iL6NYVzL=bounces-321255@domain.com
(host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user@domain.com.br> (in reply to end of DATA command))
user@domain.com.br
DC07D26A55 84919 Tue Feb 3 11:12:29 0100019c23d8f34b-c9c6d85a-eb76-4aa4-abfa-2780936b3aa0-000000@ses.domain.com.br
(host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user2@domain.com.br> (in reply to end of DATA command))
user2@domain.com.br
When I force the queue with `postqueue -f`, the following appears in mail.log.
2026-02-04T15:23:15.280271-03:00 pmg4 postfix/lmtp[183192]: D76C12740B: to=<user@domain.com.br>, relay=127.0.0.1[127.0.0.1]:10024, delay=72044, delays=72026/3.8/14/0.02, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user@domain.com.br> (in reply to end of DATA command))
2026-02-04T15:23:18.413163-03:00 pmg4 pmg-smtp-filter[183254]: 2026/02/04-15:23:18 CONNECT TCP Peer: "[127.0.0.1]:44370" Local: "[127.0.0.1]:10024"
2026-02-04T15:23:18.471585-03:00 pmg4 pmg-smtp-filter[183254]: 2238269838E966F601: message has ambiguous content: ERROR
2026-02-04T15:23:18.472176-03:00 pmg4 pmg-smtp-filter[183254]: fast exit because of errors (free 288780288 bytes)
2026-02-04T15:23:18.474580-03:00 pmg4 postfix/lmtp[183209]: DC07D26A55: to=<user2@domain.com.br>, relay=127.0.0.1[127.0.0.1]:10024, delay=101449, delays=101428/3.8/18/0.02, dsn=4.4.0, status=deferred (host 127.0.0.1[127.0.0.1] said: 451 4.4.0 detected undelivered mail to <user2@domain.com.br> (in reply to end of DATA command))
2026-02-04T15:23:18.722638-03:00 pmg4 pmg-smtp-filter[183256]: 2026/02/04-15:23:18 CONNECT TCP Peer: "[127.0.0.1]:44378" Local: "[127.0.0.1]:10024"
2026-02-04T15:23:18.787487-03:00 pmg4 pmg-smtp-filter[183256]: 2238369838E96BAC1B: unable to parse message - part did not end with expected boundary
2026-02-04T15:23:18.788134-03:00 pmg4 pmg-smtp-filter[183256]: fast exit because of errors (free 288780288 bytes)
pmgversion -v
proxmox-mailgateway: 9.0.0 (API: 9.0.4/f3ea3fa12b03, running kernel: 6.17.4-2-pve)
pmg-api: 9.0.4
pmg-gui: 5.0.4
proxmox-kernel-helper: 9.0.4
proxmox-kernel-6.17.4-2-pve-signed: 6.17.4-2
proxmox-kernel-6.17: 6.17.4-2
proxmox-kernel-6.17.2-2-pve-signed: 6.17.2-2
proxmox-kernel-6.14.11-5-pve-signed: 6.14.11-5
proxmox-kernel-6.14: 6.14.11-5
clamav-daemon: 1.4.3+dfsg-1
ifupdown2: 3.3.0-1+pmx11
libarchive-perl: 3.7.4.1
libjs-extjs: 7.0.0-5
libproxmox-acme-perl: 1.7.0
libproxmox-acme-plugins: 1.7.0
libpve-apiclient-perl: 3.4.2
libpve-common-perl: 9.1.7
libpve-http-server-perl: 6.0.5
libxdgmime-perl: 1.2.0
lvm2: 2.03.31-2+pmx1
pmg-docs: 9.0.5
pmg-i18n: 3.6.6
pmg-log-tracker: 3.0.1
proxmox-mini-journalreader: 1.6
proxmox-spamassassin: 4.0.2-1
proxmox-widget-toolkit: 5.1.5
pve-firmware: 3.17-2
pve-xtermjs: 5.5.0-3
zfsutils-linux: 2.3.4-pve1
