I had something like this happen and it was because I was using spamassassin and spamfilter.sh file was moving files around and setting the file permission incorrectly...

Webmail (apache user could not access the mail and it gave an error similar to that)

But check the mail log to be sure.

Cha Yang

-------- Original Message --------
Subject: Re:[Dovecot] Reconstruct a corrupted mailbox
From: Fatou Ndiaye <fatou.ndiaye@sentoo.sn>
To: 'Dovecot Mailing List' <dovecot@dovecot.org>
Date: 9/7/2006 11:16 AM

We're talkink about "corrupted Mailbox" because when we try to acceed via
webmail we have this message:
ERREUR : Impossible d'achever la requête.
Requête : SELECT "INBOX"
Raison invoquée : Internal error occurred. Refer to server log for more
information
We had the same problem when we were using cyrus but after doing
.../cyrus-imapd/reconstruct it works well. 

-----Message d'origine-----
De : dovecot-bounces@dovecot.org [mailto:dovecot-bounces@dovecot.org] De la
part de Timo Sirainen
Envoyé : jeudi 7 septembre 2006 17:45
À : Dovecot Mailing List
Objet : Re: [Dovecot] Reconstruct a corrupted mailbox

On Thu, 2006-09-07 at 17:28 +0000, Fatou Ndiaye wrote:

Hi all,

How can we reconstruct a corrupted mailbox with dovecot ?


What is a "corrupted mailbox"? There's no such thing really with mbox or
maildir. Except if mbox doesn't begin with a valid From-line, then it's
treated as not a valid mbox..

Dovecot's index files might get corrupted, but normally they're fixed
automatically. If not, just delete them and they get rebuilt.