I encountered an issue today where Dovecot crashed and didn't restart. This resulted in every inbound email bouncing, without queuing them anywhere:
postfix/lmtp[549]: BD61F1E12A6: to=<xxx>, orig_to=<xxx>, relay=none, delay=1.7, delays=1.7/0.01/0/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=dovecot type=AAAA: Host not found)
postfix/bounce[550]: BD61F1E12A6: sender non-delivery notification: 270421E78E6
postfix/qmgr[392]: BD61F1E12A6: removed
It's not clear why it shut down; the log just shows it quitting but not why it quit:
Sep 6 08:25:55 812a5f48a1f4 syslog-ng[116]: syslog-ng shutting down; version='4.8.3'
2026-09-06 08:25:58