Interesting info about missing blocks in the mail

I was reading up on different kinds block swaps this morning and came across some good advice. A few of my blocks recently went missing and I was puzzled as to why. I didn't put anything in with the block itself, just the address on the outside of the envelope. I think that's where I went wrong. If an envelope gets caught or torn up in the machinery and there is no info on the inside, then the block never makes it to its destination nor is it returned to the sender. From now on, I will be sure to put something inside the envelope with the block with who it's to and who it's from.