I have a dovecot server and several outlook clients. I have set the clients to use pop3 with leave mail on server (lmos) For some reason, every time the client sends and receives, it downloads every email, agan, and again. I'm guessing that there is something wrong with the tag info, but is it a server issue or a client issue?

We aren't going to use imap, because i don't feel like explaining, to already stupid users, how it works or why their mail isn't in their "inbox"

I can't claim to know the POP protocol all that well, but since it is normally used where it is downloaded and deleted (or is it "flushed"?), the behaviour you are describing isn't all that surprising. POP just isn't designed for centralised storage is it?

I'm having this problem right now too. It's something to do with the way Dovecot implements message IDs, and Outlook making a hash of things.

The Dovecot Wiki states that you need to change (or add) the /etc/dovecot.conf parameter:

pop3_uidl_format = %08Xu%08Xv

Which should make it function correctly. Unfortunately, the version of Dovecot I am using (0.99.11 on CentOS 4.5) does not appear to support this configuration option. All I have is:

pop3_uidl_uw_compat = no

which is commented out, and apparently "makes transition from UW to Dovecot smoother and avoids re-downloading mails". This option isn't described at the Dovecot wiki, so I can only assume it's been deprecated.

I really don't want to go to the hassle of upgrading dovecot on this box as it's only a temporary solution. I've uncommented the line, but I've got no idea if it will fix the problem with Outlook I guess I'll find out tomorrow when the customer starts bleating about their deleted e-mails not deleting.