While we've identified some red flags for you before, let's add a few more, shall we?
If the email refers to the patch you "must" download as "a mod one" then it might not be real.
If they have moved said patch to an external website, then you might want to worry.
If the reason for the move is because, "recently, Hackers have been trying to crack our folders and steal every future project" then it is time for you to roll on the ground laughing. Just hope that Hackers don't team up with the Boogeyman, or Terrorists!
If you are referred to as one of their "lovely members who do not understand" you should get a medal, really. Their repetitiveness is dizzying. Luckily, they will "explain it shortly" for you. I think someone needs a thesaurus (or a brain).
The best part? To participate, you have to upgrade your account by sending them your account details, which Blizzard will never ask you for, and of course, your Beta key code. Just send it to an email address that ends in @live.com, and you're set!
Never mind that you're supposedly testing during the Gold phase. All those bug reports you'll be logging with the "/bug command" will be terrifically helpful while they're burning the discs.
Now, you'll be playing the same characters you used in the Beta, except you're not allowed to copy characters over. Have fun with that.
Their final plea? "Please do not delete this e-mail, or show it to anyone else." Most likely this is because they seem to be targeting very slow eleven year-olds, and showing it to someone else might get the poor kids teased. They just care about you, really.