If the receiver of a package from me ends up cussing while trying to open it, then I know I have properly prepared the package for shipping.
A knife should NEVER repeat NEVER be sent in an envelope of any sort. And under no circumstances should a fixed blade be shipped unsheathed. If no sheath is available, HEAVY packaging needs to be around the AFFIXED to the knife in such a manner that said covering CANNOT come loose.
Has anyone else ever watched some of the videos about the automated handling of mail by the USPS?
Some of the drops from conveyor to a catch bin or to another conveyor can be 6 to 8 feet. Then other packages land ON TOP of the previously dropped packages. Unprotected or improperly protected fixed blades can and have been driven through envelopes, bubble-wrap envelopes and boxes. I've received dozens of knives with points driven through the packaging, including several where the points were sticking out at the PO. The postmaster was less than pleased.
The machinery that handles envelopes squeeze them through very narrow "slots" between rollers can put as much as 100# per square inch of pressure, easily cracking plastic or celluloid knife handles/scales.