Well, I dont know why on earth you wouldnt put a return address on an envelope containing cash? Sure some guys say not to, but hell, its not illegal to send money to someone. Just use your head and dont list out in the envelope what the money is for....which I might add people do all the time, blows my mind. Technically speaking I beleive you are supposed to declare whats in it and its value if its anything but paperwork. Most countries let letters under a pound sial right through. If I was sending cash theough I wouldnt declare it, just tempts some poor postal worker to snag you letter.