[craftyguy]

you can just ask your recipeint to send you some uuid on the letter after they receive it. i have no idea what problem you are trying to solve though.

[y4mi]

i once heard of a case were the employer send an unrelated document to an employee.

later on, the payment stopped and the employer claimed that they fired him at that time.

I don't recall how that case ultimately turned out, but maybe something like that? would be incredibly rare though and of dubious worth for mostly anyone

[craftyguy]

I believe there are courier services that help guarantee document delivery to the correct person, i.e. for sending/serving court summons.