Bubble mailers are the way to go. Extra padding and they don't go through the same sorting machine that normal white envelopes are processed through. At $1 a bubble mailer, it's not really breaking the bank and gives extra protection to cards. If you buy it in bulk (100 bubble mailers) it comes out to be 0.40c each. A simple way of looking at it, would be, would you be happy receiving your cards in a bubble mailer that provides extra protection, or a white envelope that could damage the cards?