How to use xbox keyboard
How to type in a e-mail address on the xbox keyboard?
I'm going to assume you mean sending an email from the xbox 360. I don't think that it's possible to send emails on the xbox360, but you can add your buddys from MSN messenger.
If you actually mean how do you type in the address, just use the normal keys on screen, when it comes to the "@" symbol use the option to show special characters (one of the triggers does this I think) and then choose from there.
I can't be more helpful though because I'm not sure of exactly what it is you're asking.