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@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?