Outlook 2003 - Default Mail Source

I have a small business server 2003 running exchange etc with several clients attached. All of the clients are running XP pro and use Office 2003 pro.

During the transitional period (until the remote sales team can be moved across) I have had to add in the old pop based email (mrouter) as a mail source, as well as the new exchange mail system on the clients outlook 2003.

To enable mail to reach the sales team (who use the pop based system) I have to make the pop based mail source the default for the users(otherwise exchange will complain that they are not in the address book), but each time the PCs are restarted, Exchange server becomes the default source. Does anyone know a way to keep the pop source the default mail source?

Thanks all

Andy.