[Dovecot] Mailbox isn't a valid mbox file

[Jay Chandler]

Keep getting this error within Squirrelmail (and other clients) on one 
particular user's mailbox file:

ERROR: Could not complete request.
Query: SELECT "INBOX.Backup"
Reason Given: Mailbox isn't a valid mbox file 

I've snipped the first and last message off of it, still no love. 

mailserver# cat FILE | od -c | less
0000000    F   r   o   m       p   r   o   m   o   t   i   o   n   s   @
0000020    e   m   e   s   s   a   g   e   .   c   i   s   c   o   .   c

So apparently there isn't a control character in the first message 
that'd be causing this either.

Anyone have any ideas?  Only one user out of many is having this issue, 
but he's whiny...

-- 
Jay Chandler
Network Administrator
Chapman University