I would at least give it a week before you send a second reminder, if you haven't already. I had a professor not respond to my email for at least a week, but he still submitted all of my letters on the same day. So there's a possibility your professor is waiting until s/he has finished writing it to respond back or any other possible reason.
As for sending documents by mail, as from what I know with the schools I applied to, as long as the mailed documents are postmarked before the deadline, it doesn't matter when they arrive. It usually takes a few weeks to a month for schools to compile their file on everyone so that shouldn't affect anything.