[Dovecot] Mailbox isn't a valid mbox file

[Cliff Hayes]

Hello all,

I have a new installation of Fedora 4 and Dovecot 1.4.Alpha4

A small percentage of my users are getting unable to pop mail from a client
(ie:  Outlook), they get continually prompted for username/password.  The
error they get is:  Mailbox isn't a valid mbox file.

When I look in the file, I don't see anything unusual.  There's not much
info on the Internet about this problem.  The only thing I found mentioned
blank lines in the file.  So, I tested and found that I'm able to get mail
on other accounts regardless of whether there are blank lines in between
messages.

Thanks,

Cliff