Unknown SMTP account on email client properties

This question is for exchange 2003. If I create a new email (blank page) got to (TO:)to pick a contact from the global address list there is an SMTP account that is not ours and belongs to a contractor. Does that means that he is getting a copy of all emails? Even if I create a new account his domain will show up at all time. However, I cannot see where this is being created. There is two SMTP email address; one is a reliable email address with our domain name and the other SMTP is for the domain of the contractor.

Can you please help?