[Dovecot] auth-worker temporary failures causing lmtp 500 rejection

Hi there,

I'm using dovecot 2.0.16 with a mysql user database. From time to time when we have a big influx of messages (perhaps more than 30 concurrent rcpt to:<> sessions at the same time so no auth-workers free?) or when we have a transient issue connecting to the database server, we see the message:

Jan 25 16:38:23 mailbox dovecot: auth-worker: sql(foo@bar.com,1.2.3.4): Unknown user

and the lmtp process returns:

550 5.1.1 <foo@bar.com> User doesn't exist: foo@bar.com

This would be correct for a permanent error where the user doesn't exist in our database, however it seems to be doing this on transient errors too. Is this an issue with the code or perhaps some setting I have missed?

Thanks,

Mark