Got that email yesterday, and it was completely legit on my end (and have seen others get it too).
Couldn't log in (actually launcher would just crash trying to, so instead went to my account and yep, restricted). The plus note on that email is the link you're supposed to follow doesn't ask for your current password and instead just resets it.
But yeah, the best thing to do after finding an email like that is just check your account yourself and remember that apparently with this temporary restriction, SE won't ask for your password.