that was lovely. Sure enough the letter writer has a wikipedia article as Paul Devlin (filmmaker)

I like the Arkell versus Pressdram.

https://news.lettersofnote.com/p/arkell-v-pressdram

There is a reference to a "small grammatical error" in the rejection from Harvard, but I did not quite understand what he was referring to.

Was that obvious from his reply and I missed the point?

I am guessing it must be in the form of "Please accept our letter of rejection" or similar?

Around 2017-2018 I remember reading a really interesting article about how the Obama White House handled letters to the president. The vast majority of letters (hundreds per day, IIRC) were answered by staffers, but each day they would select 10 letters that Obama would read himself. He didn't personally write out a reply, but he'd make notes for the staff about how he wanted to respond. No idea how Reagan's team handled it, but it's at least possible that he was personally involved in the reply.

Social media has ruined our faith in kindness