[Dovecot] Next message unexpectedly corrupted in mbox file

[Justin Piszcz]

Hi,

I am seeing this on one of my servers:
Jan  8 10:08:58 l1 dovecot: IMuser(user): Next message unexpectedly corrupted 
in mbox file /home/user/Mailbox at 10558

I have never seen this before, and google yields no results except when 
this warning was added to the source code here:
http://www.dovecot.org/list/dovecot-cvs/2009-December/015177.html

The user has deleted all of the mail in the Mailbox but the problem 
persists.

Any ideas?

Justin.