email question

I've had the game pop up in Steam before even checking my emails some days.

If nothing else, I will follow this instruction

Gifts will be sent here. For the first time in history, use your real e-mail address

Yeah this is true. When you click the link in the e-mail it will open your Steam account to activate the game, requiring a log in. Doesn't matter where you click the link from or what e-mail. IIRC you can even copy+paste that same link in any chat, or whatever and whoever clicks it will be able to activate the game.