Timeout quota exceeded

Hello,

out of nowwhere, suddenly my delivery queue fills up with error messages:

maildrop: Delivering to /dev/null
maildrop: Timeout quota exceeded.

The mail is transported to maildrop via postfix.

The filesystem quota is not at the limit.
The user does not do anything non-standard in his .mailfilter.
There are no NFS mounts involved.
The load is below 1 on a 4 core system.

In http://courier-mail-server.10983.n7.nabble.com/maildrop-Timeout-quota-exceeded-td23394.html there is a file
"maildirsize" mentioned, but this file can't nowhere be found.

All maildirs of the users are 4.5 GiB in total, with the largest one 3.3 GiB.

System is Debian Testing.

I'm grateful for any ideas!

Florian


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