Well, my son's 9 and I set him up an email addy about 3 years ago because some of our friends (and their girls) moved far away from us. Both our families have been working on teaching the kids about the computer and internet, so we encourage them to type out emails to each other. My friend's two girls are the only people who have his address and I have it set up so that any email he gets automatically sends a copy to my address as well. The kids are all pretty sweet and innocent, so I haven't had any problems. Though they probably only contact each other 3-5 times a year.

Its kind of a hard choice. On the one hand, I would ask if you listen to his phone calls? If not, why check his emails? On the other hand, I know there is fear that kids may be talking to strangers, so I would definitely understand being afraid of that. On the other hand (I have many, many hands apparently!) I am glad that the two of you have a good enough relationship that he asked you about it without just making one for himself and not telling you about it. Of course, you know your son best, but maybe you could take it as a sign that he talked to you about it in the first place that he's ready to use email in a responsible way. If you are really nervous, you can set up through gmail (I don't know about other services) two email accounts, one for yourself and one for him. When you set his up, you can go into the preferences and set it to email you a copy of all incoming messages. You could try just glancingly monitoring it like that for a while (not exactly sneaking, but maybe just keeping an eye on things until you are comfortable).

Also, if he doesn't sign up for any website's newsletters or just type in his email address willy nilly, I doubt he will get spam. I've had the same email address for 6 years and maybe get one piece of spam every 2 or 3 months.