We have a setup with a Small Business Server 2008 that is "popping" (that is what we call it) mails from a external mail provider.
It's using the built-in pop3connecter to download mails to it's internal exchange.
The clients are running Outlook 2007, and are connected to the exchangeserver on the SBS 2008.
However, now they get prompted to login the the "external" name of the SBS server.
The one that was defined in the "connect to the internet" guide.
In this case it's job.siemsens.dk
This came after a Windows update i think.
The prompt hits the users every 5 minutes, and it's very annoying for them.
If they hit cancel, everything works, they can send and recieve emails without problems.
But the prompt comes back.