It sounds like there's more going on than just the confusion with the mail. I found myself getting into arguments with my mother about small things when I know now that my problems with her weren't about that.

You're a jerk (putting it mildly) - she doesn't know what is in the envelope but wants to make sure that you're not missing out on something - perhaps a letter from a classmate. Yes,she could simply put it back in the box but then she wouldn't be able to interact with you. And if that's the worst thing possible for a precious little princess - tell her so and it has nothing to do with her age - it's all about you. I'm glad that we're not related.

At 80+, many begin to suffer cognitive degradation.

Relationships at this age are really complicated. There’s an incredible amount of history that we are not privy to. Take a step back and try to see the relationship from the outside. Parents are products of thier parents and don’t always have the best skills or coping mechanisms. A little understanding goes a long way.

Your Mom is 80, probably not much longer to live.
She is obviously trying to reach out to you, using this mail as a pretext.
I promise, when she is gone, you will suffer a lifetime of unrepairable regret for not treating her as you would a stranger on the street...

Wow..you're not a very patient or kind person, are you? I doubt I even remember how the US mail works after I've been in Thailand since 2010 and seldom get mail.

I sure hope your mom has other children who are more loving than you are. You sound like someone I should block, actually.

My mom ... And dad ... Died when i was ten ... I wish i still had them ... But especially my mom... Im sad you don't like your mom.. But do you hate her ?

From the mom side of the situation, there are times when I've called or emailed or texted just to make contact. I try not to do it too often because I don't want to be a bother -- or be perceived has having dementia. Also from the mom side, I just need to ask why you sound to me so angry about your mother. My mother and I had a deeply conflicted relationship but I did answer her calls -- even if I realize now I could have been nicer to her. And I wish I had been. (Please understand that I know you may have absolutely legitimate reasons for not wanting to be in contact and I'm not trying to be 'judgy'. I'm just trying to offer a different perspective from an old (70ish) mother's position)

My mom does this at 59. I truly believe she's lonely. Divorced from my father, no real social life. She will call or text with the smallest things. Sometimes I know she should know the answer, and I wonder if she is getting early on-set dementia.