After about three years of this, it seems I have finally gotten somewhere near to the bottom of this.
The symptom:
Suddenly a user cannot download their email. Checking again through SquirrelMail, I get an error which says a log was written.
Going to the logs I see
"imap(username): Error indexing mbox file /var/mail/username: LF not found where expected"
Using Webmin's read mail module, I can see the messages. So, I move them to another account, but this is not yet the end of it. I was at first having to delete the mbox and then I'd send a test message in to recreate the mbox. But today, I tried a different tack.
I opened the now empty mbox in vi and found one blank line (LF). I deleted that line and then moved the mail back in and everything was fixed. So the line was still left behind.
The next time this happens, I'm going to try to delete a LF from the top of the mbox file to see if it is fixed without moving the mail.
I have read several places, although this is extremely difficult to track as there seems to be a multiple from address issue for some releases.. but anyway, I did finally find that dovecot .99 has an issue with leaving behind an extra linefeed at the beginning of the mbox. Deleting this linefeed fixes the problem. Supposedly dovecot 1 has fixed this problem.
I have found many reports of problems on Fedora and RedHat. Also, Debian has a closed bug report regarding this issue as they have moved forward to dovecot-1.0 and it doesn't have this bug. The issue seems to not have any relation to the mailserver, as I saw both reports of problems on at least Sendmail and Postfix.
Why are we still bugged with this? Seems that this is a bug that RedHat should be aware of?
The problem is it only rarely happens. I have no idea how to repeat the issue. It always seems to be an Outlook user, although that is by far the most prevalent email client in use by our users and it might just be chance.
So, what to do from here? Bug report to RedHat? This is most irritating! I can't even guess how many times I've fixed these mboxes. I'm about ready to toss dovecot in the trash until 1 becomes the RH standard unless there is a fix or upgrade from Redhat.
Thanks, John Hinton