Quote Originally Posted by Nochowderforyou
Just put the money inbetween a folded sheet of paper. You can put it in anything, but just make sure you cannot see money through the envelope, or a mail carrier will get sticky hands and take it. Just don't send change, or that's a good bet it will not make it.
This is pretty much all you need to do. Get a box of 'security' envelopes from the market so people can't see through it. When you put the money in, just fold a piece of paper like it was letter and put it in there to further obscure it. Unless someone is sniffing the envelope to find money, you should be OK.

Just in case, you might want to get a delivery confirmation also. It could make it to its intended destination then all of a sudden the person you're dealing with is like, "Huh? You didn't send me no money"