This is just a tip; not too important. I searched and I don't think it's a repost, but if it is, sorry.
Basically, what you do is log into their account on the official WoW forums, and then click "Options." Blizzard, for whatever reason, implemented a little email box there, even though it's not actually used. Funnily enough, if a player inputted their email in that box, anyone who logs on the account can see it.
So, basically, just log in to the forums, click Options, and look at the box that says "Email", and if the person put their email there earlier, you will see it. It isn't censored like it is on the account management page.
This can be helpful if you want to send fake emails to the person or whatever.