DNQuest, although a C&D can be sent Via email, it will most always be followed by a Certified letter. Anyone can send you an email, a C&D sent via Certified mail would be sent on a company letter head. There is a chance that the email is a scam, as it's been done before. I'm not suggesting that you fight this battle. You have to choose your battles. If you registered the name in bad faith, or it means nothing to you; get rid of it. Even if its not a real C&D then push the obligations off on someone else. If you hold dear to the domain name, wait for the certified letter. Then send it over.
Im not an expert, and you should make your own decisions. I am just giving you my advice as best as I know how.