I've never done a NPN and decided to bring some envelopes to work to fill some out and I saw it said somewhere you need a #10 envelope. Are you allowe to use the bigger business envelopes or will they not accept that?

They more than likely won't except it. I sent off a few myself and I used #10 envelopes though. When I first read a post about how to send them a few people said they are strict so I would only send a request in a #10 envelope.

Thanks for replying! I'll just get a box of the right ones.