Can't remove unwanted mail account in Preferences

On my network, I have a MacBook Pro running Snow Leopard and a Mac Mini running Snow Leopard Server. I had previously activated Mail services on the SNS machine which automatically pushed an email account to the MBP - so alongside my regular Apple MobileMe and Gmail accounts in Apple Mail, I have a greyed out email account provided by Snow Leopard Server.

However - I have since turned off and disconnected the SLS mac Mini from the network (after turning off the Mail service). I now have a greyed out email account on my MBP - obviously I have tried deleting it under Preferences > Account but it is removed for a moment and then re-appears. It does this regardless of if the MBP is on the network so something locally is forcing this email account to remain in Apple Mail.

Any ideas anyone?

Thanks.