If they have an IP address they can trace which private or public entity its leased or assigned to. They can then come up with a domain name (*@user.com, org, etc.) thats about all they can find out since its against the law for AOL, Yahoo, or local cable and phone internet providers to give out your personal info to unauthorized persons including your name.
I think the only people that need to worry are people who have actually emailed any of the branches or Patterson, Brooklyn with that domain name since then they could simply match it up. This is still circumstantial evidence though since for example there are millions who use Yahoo email.