Addendum: Yesterday’s periodic change of /etc/machine.secret unfortunately caused us another failure (with mail loss, because postfix/lmtp is bouncing and NDN / backscatter is not allowed, even the sender is not informed about non-delivery), because the corresponding integration script for the secret change was missing here as well.
Solution: Kopano ldap problem
This should (actually) not happen with supported systems/versions.
How can one actually achieve that with such errors/failures of the delivery agent (here Kopano) mails are lost by bounce & NDN / backscatter prohibition? So either Postfix does not accept anything from external in such cases anymore or there would be a backup(queue). Should Postfix not bounce with “hard” 500 errors and discard them with such errors within the internal mail cascade?
Feb 11 08:38:38 metis kopano-dagent: Failed to resolve recipient email@example.com (0)
Feb 11 08:38:38 metis kopano-dagent: Requested e-mail address "firstname.lastname@example.org" does not resolve to a user.
Feb 11 08:38:38 metis postfix/lmtp: F149F5F98B: to=<email@example.com>, relay=127.0.0.1[127.0.0.1]:2003, delay=0.18, delays=0.06/0.01/0.07/0.05, dsn=5.1.1, status=bounced (host 127.0.0.1[127.0.0.1] said: 503 5.1.1 User does not exist (in reply to RCPT TO command))
Feb 11 08:38:38 metis postfix/cleanup: 2614E5F999: message-id=<20190211073838.2614E5F999@metis.xxxxxxxxxx.local>
Feb 11 08:38:38 metis postfix/bounce: F149F5F98B: sender non-delivery notification: 2614E5F999
Feb 11 08:38:38 metis postfix/qmgr: 2614E5F999: from=<>, size=3844, nrcpt=1 (queue active)
Feb 11 08:38:38 metis postfix/qmgr: F149F5F98B: removed
Feb 11 08:38:38 metis postfix/smtp: 2614E5F999: to=<prvs=938f25d5b=Pk@yyyyyyyyy.at>, relay=bsmtp.a1.net[18.104.22.168]:587, delay=0.2, delays=0/0.01/0.17/0.02, dsn=5.7.1, status=bounced (host bsmtp.a1.net[22.214.171.124] said: 550 5.7.1 <unknown[126.96.36.199]:18
974>: Client host rejected: sending backscatter not permitted (in reply to RCPT TO command))
Feb 11 08:38:38 metis postfix/qmgr: 2614E5F999: removed