Recruit-A-Friend Email not sending?

I've got a friend who's been waiting an hour, and hasn't received the recruitment email I sent him. We know he can receive emails from SE, because he played FFXI, and still gets SE emails, so that's not the issue. Is this normal, or do we have a problem?

I knew it wouldn't be long after I asked about it that it would show up. Still clocked in at over an hour. Wow.