[Dovecot] Error: corrupted index file

Hi all,

I see the next error at dovecot.log:

dovecot: Sep 06 17:57:27 Error: IMAP(jordi.espasa@opengea.org): Corrupted index file /var/vmail/opengea.org/jordi.espasa/.Dov ecot/dovecot.index: Duplicate header extension keywords

¿Why this error is producted?

-- Thanks, Jordi Espasa Clofent