[ALUG] Evolution downloads duplicate emails each time it connects to POP server

[sagr]

Hi Folks,

I have recently installed Ubuntu 7.04 and am using the Evolution mail
client version 2.10.1 to access my POP server hosted by 1&1.

I access my emails via two PC's (one running Windows, the other Linux)
so have set Evolution (on my Linux PC) to "Leave Message On Server" so
they are available to download on my Windows PC (I currently use Windows
as my main PC but just want occasional access to email on my Linux
PC).  

The problem is that when I tell Evolution to "Send & Receive" it
downloads all the emails on the POP server even though it has already
downloaded them earlier.  I am therefore downloading a complete
duplicate set of emails each time I do a "Send & Receive" filling my
Evolution inbox with multiple copies of the same emails.

Is this a problem with Evolution, Linux, my ISP's POP server, or just
because I have incorrectly configured something?

Any suggestions welcome!

Sagr.