dovecot - Jan 2010 - Modifying the underlying maildir externally (webmail, replication)

Hello,

I have a setup where there are multiple maildir users, one of them being 
the pop/imap server itself, the others are for example a maildir capable 
webmail and message replication.

I would like to evaluate Dovecot, but I wonder how would its binary 
indexes and logs fit into this picture.

After running through http://wiki.dovecot.org/IndexFiles I'm not sure 
how well would Dovecot work with other programs modifying the maildirs 
(adding, deleting, moving messages, folders etc).
The "Main index" section says "The index file is synchronized
against
mailbox only if the syncing information changes.", where syncing 
information consists or cur and new directories' timestamps.
Does that mean I am safe there?

The cache file is hopefully just a cache, so it won't contain 
information from messages which are inserted or moved by an external 
program, and I assume Dovecot fetches the message lists and other 
information from the main index, which seems to be OK.

The transaction log is for the main index, so if the latter is OK, the 
former should be OK too.

http://wiki.dovecot.org/MailboxFormat/Maildir talks about MUAs and there 
nothing scary can be found, except for some temporary conditions, where 
the changes won't propagate to Dovecot in real time, but it's OK.

Are the above right, and can Dovecot use its indexes and caches safely 
with others using the same maildirs?

Thanks,

On 20.1.2010, at 22.21, Attila Nagy wrote:
> After running through http://wiki.dovecot.org/IndexFiles I'm not sure
how well would Dovecot work with other programs modifying the maildirs (adding,
deleting, moving messages, folders etc).
> The "Main index" section says "The index file is
synchronized against mailbox only if the syncing information changes.",
where syncing information consists or cur and new directories' timestamps.
> Does that mean I am safe there?
Yes. The worst that can happen is that Dovecot doesn't see external changes
for 2 seconds. And that's only if your filesystem doesn't support
sub-second timestamps.
> Are the above right, and can Dovecot use its indexes and caches safely with
others using the same maildirs?
Yes. I've only recently added maildir_very_dirty_syncs=yes that improves
performance but makes it work less safely when other programs modify the
maildir.

Although there is kind of a potential problem if other programs modify the
maildir without locking. http://wiki.dovecot.org/MailboxFormat/Maildir#Locking
but that isn't unique to Dovecot. That would cause problems with all
programs accessing maildir. Dovecot just logs an error about it, instead of
silently giving broken information to IMAP clients.