If I mail anything in a manila envelope, I essentially rebuild it and completely cover all 4 edges with clear packing tape as well as the entire label and then just for good measure I wrap a couple of lengths around the envelope both ways. Plus I enclose in ziploc bag inside with address info. My first ebay order was a yrs worth of an older quilting magazine and he didn't reinforce the edges and half the magazines went bye-bye, he replaced them, of course, but I've never trusted manila envelopes again! If I can recycle a used Tyvek envelope I will, but I tape those suckers well as well. Tape is cheap enough and I swear the PO plays football with packages sometimes.