Entourage keeps re-downloading emails!

[myuserid08]

I have a problem, entourage keeps downloading all emails from my pop account (all 6000 of them!!!).

I'm running:
Latest entourage
Latest snow leopard
Its a pop account
Entourage is set to leave a copy on the server.

Is there a way to stop it re-downloading all emails from the account or do I need to let it download and (hopefully) it will sort itself out

Thanks