You don't get 'big explanations' here - you get the free cliff notes version. Especially given that there is at least one big problem in this scenario that is rather glaring*.
- Your ad is likely still considered to be an 'invitation to treat', rather than an offer, based on my gut feeling.
- In any case, it causes problems that you've put "the first person who sends a notice of writing" - rather than 'the first written notice' I receive. If I posted my notice a week before someone else, but it got delayed in the mail and you received their notice first, shouldn't I get the car because I sent my notice first?
- By including your address in the ad, this conveys that that is the method which is supposed to be used for communication.
- Electronic communications legislation tends to revolve around explicit consent by the parties to the use of the medium - I don't see that here. Having no mention of an email address strengthens the proposition that email is not an acceptable method of communication for the transaction.
- There should be no reasonable expectation from your friend that the email is (a) appropriate, (b) reliable or (c) still current.
Accordingly, my thoughts are that on the face of it you're not bound by any contract to your friend.
* Given that you've said your friend only knows how to contact you by the email address, and you don't use that email address (or apparently have access to it), how would you even know he contacted you via the email address?