Unknown Internet Connection

Looking through our Firewall logs, it appears that our Exchange connector server is trying to connect to an unknown internet address every 60 seconds or so. (I say unknown as I can't find any reference to it in the RIPE database). I've checked theIMS queues and there's no mail waiting to be delivered and I've stopped all non-essential services but the server still tries to connect to the address.

The big question: Is there any command or tool I can use to find out what is causing this connection to initiate?

TIA,

Kris

ps - I've also done a full virus scan on the machine just to ensure that there is no remnants of Nimda on there.