Problem delivering to shared folders

[teardrainer at web.de]

Hi all,

we recently migrated our system from CentOS to Debian10 and apart from a few glitches everything went well. However today we noticed that mail delivery to shared folders is not working. We get the following error from postfix/lmtp:

status=bounced (host kolabng.ourdomain.com[/var/lib/cyrus/socket/lmtp] said: 550-Mailbox unknown. Either there is no mailbox associated with this 550-name or you do not have authorization to see it. 550 5.1.1 User unknown (in reply to RCPT TO command)

It seems that cyrus cannot find the target mailbox. We are at loss what could be causing this since everything should be the same as on the old system.

New System:
postfix/lmtp[7379]: B2A8C1B3E: to=<shared+shared/Customers/Big Blue Company/Orders at ourdomain.com>, orig_to=<shared+shared/Customers/Big Blue Company/Orders at ourdomain.com@ourdomain.com>, relay=kolabng.ourdomain.com[/var/lib/cyrus/socket/lmtp], delay=0.09, delays=0.04/0.03/0/0.02, dsn=5.1.1, status=bounced (host kolabng.ourdomain.com[/var/lib/cyrus/socket/lmtp] said: 550-Mailbox unknown. Either there is no mailbox associated with this 550-name or you do not have authorization to see it. 550 5.1.1 User unknown (in reply to RCPT TO command))

Old System
postfix/lmtp[10067]: B7F246037F75: to=<shared+shared/Customers/Big Blue Company/Orders at ourdomain.com>, orig_to=<shared+shared/Customers/Big Blue Company/Orders at ourdomain.com@kolab.ourdomain.com>, relay=kolab.ourdomain.com[/var/lib/imap/socket/lmtp], delay=0.1, delays=0.03/0.02/0/0.05, dsn=2.1.5, status=sent (250 2.1.5 Ok SESSIONID=<kolab.ourdomain.com-9752-1589896134-1-10296900818814903381>)

The only thing I noticed is that on the old system the target mailbox has the FQDN of the mailserver at the end, whereas the on new system it simply ends in the domain:
orig_to=<shared+shared/Customers/Big Blue Company/Orders at ourdomain.com@kolab.ourdomain.com>
orig_to=<shared+shared/Customers/Big Blue Company/Orders at ourdomain.com@ourdomain.com>

Any help or hints to what might be causing this would be greatly appreciated.


Thanks,

Bob