The fact that I received it at all is due to how it was packaged. In case you can't tell, the envelope came directly from the US Postal Service and the highlighted text on the envelope says "Found Loose in Mail." Apparently the packaging that this block was sent in was destroyed, but it still managed to get to me because the sender enclosed the block in a plastic bag and included my name and address on a sheet of paper inside.
Now you may be thinking that you always package your blocks really well. And you probably do, but to give you some perspective, the block above was mailed in a padded Jiffy envelope. I never would have thought there would be an issue but you just never know.
So here is my best practice for sending your blocks. Once they've been pressed, fold them and place them into a ziplock bag, a bag that you can tape shut, or even some Press'n Seal. Include a note or sheet of paper that has the recipient's name and address clearly visible.
If it's a slider ziplock type of bag, you might also consider taping the zipper down against the bag using some packing tape, as some of those slider zippers can be rather bulky and could rip your envelope when going through the mail system's sorting machine.
And there you have it - my best practice to ensure that the blocks you work so hard on get to their intended recipient.