Since your son is asking for your permission to have an email, then he shouldn't be putting conditions IMO. My oldest girl has had one since she was 10 and I just told her this is how it would be - I would have access to it. I also taught her about internet safety - not giving out personal info. I rarely check on it now, because she has earned my trust, but I could still look if I wanted. Funny thing is, I wouldn't mind if she had access to my email either - I have nothing to hide lol.
She started a Facebook account a few months ago and she knows I can see her page. I've browsed at other kids accounts and I wonder if their parents look, because some of their photos are inappropriate and the language is awful. You're the parent Sabrina and you make the rules.