Never trust the sender showed, the easiest way to find out if a mail is fake is mouseover the link given in it and check if it's not some made-up mispelled http address (worlofwrcraft, batlte.net, wow-admin-trust-me-this-is-real.com and these kind of crap). That's not 100% sure but still...
If you wanna be really sure, just check your battle.net account through the official website (beta invites and important stuff will be notified there someways).