It's not. The whole concept of 'read receipts/tracking' in general, whether it's email or messaging or whatever is starting to get to me.
I've never actually heard of a positive use for them and I know they've personally caused me stress before as well as people I know and people's stories i've read.
I honestly can't see the desirability about a feature that allows you to see when others have read your message.
Even in your examples, they cause stress, the marketer and the love letter writer are stressed waiting, the person receiving the letter if they knew reads were being tracked would be stressed.
It really creates a strange conversation dynamic and the more communication methods that have it, the more uncomfortable I find communicating to be.