Postfix lock file without permissions

[Petr Kuchyňka]

Hello,

our postfix installation suddenly started to create a lot of deferred messages. I would like to ask anyone for help.

It produces this error:

Jan 8 12:52:27 mailserver postfix/virtual[12073]: 1E4FD6228A2: to=``abuse-notifications@...``, relay=virtual, delay=89639, delays=86872/2749/0/18, dsn=4.2.0, status=deferred (delivery failed to mailbox /var/vmail/.../abuse-notifications: unable to create lock file /var/vmail/.../abuse-notifications.lock: File exists)

The lock file exists, but it is being created without permissions so postfix is then unable to delete it when not needed:

---------- 1 vmail vmail 0 Jan 8 12:54 /var/vmail/.../abuse-notifications.lock

Stopping postfix, removing the lock file and starting it again helps for some amount of time, but then it occurs again.
I have tried to set the lock file some permissions - postfix deletes it immediately and creates a new lock file without permissions.

Postfix version: 3.3.0-1ubuntu0.4 amd64
OS: Ubuntu 18.04.6 LTS

Thank you for any ideas!

Petr