[Dovecot] Error: write(auth socket) failed: Broken pipe

Hello

From time to time I'm seeing errors like this in my logs:

Mar 16 10:45:55 box5 dovecot: lmtp(5438): Error: write(auth socket) failed: Broken pipe

This causes delivery from postfix to fail until I restart dovecot.

There doesn't seem to be any other messages in the logs related to this error. Has anyone ever seen this error?

Thanks Andre