I just wanted to post and let everyone know about mail sorting machines. I am a machine mechanic at the Post office and see every single day how things get caught in the machines. If you put a rigid item like coins, pens, memory sticks, etc, it may not make it through. Sometimes it gets stuck and other times just gets torn from the envelope. If you want to mail coins please use a bubble mailer. It will go on a different machine that can handle stiff items.