On Fri, 2007-03-16 at 10:41 -0400, Justin McAleer wrote:

deliver logs the error in the subject whenever the userdb lookup fails. I had a query discrepancy between postfix and dovecot, so messages were accepted that shouldn't have been, but I figured deliver should probably handle that a bit more gracefully :)

This happens only if you're using auth cache. Fixed a few days ago: http://dovecot.org/list/dovecot-cvs/2007-March/008123.html