send ram in a plain envelope. That's never a good idea, even if you have never had any problems.
A padded envelope with the memory in it's original packaging is OK. The best way if you don't have the original packaging is to put them in an anti-static bag, wrap them in bubble wrap, and place them in a small box. You could also use packing peanuts instead of bubble wrap. The post office will have a nice selection of boxes you can buy. I've used the boxes that personal checks from the bank come in.