Just take it to the post office and they will tell you. You don't want to not put enough stamps on there and it doesn't get there! I also sent mine so that I'd get a return receipt. It's good to get that confirmation and you aren't stuck worrying. Good luck to everyone applying this year!!
ok, not to be too "simple," but why not just send the secondary via regular mail? whether they send me a postcard confirming receipt or i call in 3 days to check if they've received it, i'll know that it's there, right? i'll probably use priority mail just because i'm only sending, like one secondary by snail mail, so it's not a big deal....but i was just wondering.