If you have any doubt whatsoever about a Blizzard email, it's a scam.
Personally, if I get any I ignore them, I'll know if there's a problem if I actually can't log in, and then I'll go to the official site and try logging in.
If that doesn't work I'll phone them.
I'm surprised these people aren't hated more however, they're essentially thieves, and they're stealing hours of someone's hobby time, it's akin to sneaking in at night and smashing a kid's model airplanes. Then selling them for a few cents of firewood.