[Dovecot] Seen flag getting lost

[Timo Sirainen]

On Tue, 2011-10-25 at 13:02 +0200, Edgar Fuß wrote:
> We have two dovecot 1.2 instances sharing Maildirs on NFS. Indexes are local to the individual servers.
> Occasionally (no idea how to trigger this), the Seen flag gets lost on some messages. I've verified that actually the ``S'' is missing from the filename.
> I suspect something like server A caching the flags, server B setting Seen, and then server A flushing its cache for another change so overwriting what B changed.

That shouldn't happen because of Dovecot's indexes. Dovecot doesn't
force Maildir to match its indexes. Whenever doing flag changes, it
stores them as "add \Seen flag to UID 1234". Then the 'S' flag is added
to the current Maildir filename without losing any other changes.