express envelopes at the 5-letter ship center are now almost all "reusable" -they have two adhesive strips, so they can be opened and used again with the second adhesive. With a bulky package, one may use the outer strip and leave the inner adhesive intact. Then, either 5-letter employees or receivers can easily open the envelope, empty the contents, and seal it back and it would appear to have never been opened. USE BOTH ADHESIVE STRIPS - trust me, I just learned the hard way. Also save your receipts if you ship in person.