[Dovecot] imap, locks, and dovecot

[Mauricio Tavares]

      Let's say I have two computers -- a desktop and a laptop --
setup to check email on my postfix/dovecot/mailscanner box by using
imap. Now, both machines use thunderbird and have a filter in that
mail client to move emails that have a certain to: address (an alias,
like support at domain.com) to a mail directory. The desktop is setup to
check for mail every minute while the laptop initially is told to do
the same.

So, I send an email to the said address. dovecot (1.1.7) puts it in
the inbox. thunderbird in one of those machines sees it and moves it
to the, say, support folder. Then, another copy of the same mail is
created and placed in the same folder. I then begin increasing the
time the laptop waits before checking mails. Up to 5 minutes I am
still having the double email issue, but if I the laptop to wait 10
minutes I only have one copy of the said email.  That makes me think
both clients are seeing the same email and moving it at the same time.
I do not know the imap commands being used but it sure seems that
there is not some kind of locking system for the mail files (I use
maildir) to make sure only one program is accessing the said email.

Am I correct? Is there a way around that?