I replied to an email with rq. The email had a png attachment. I edited the quote down to the relevant section and sent the email. The recipient replied and said that my email had an Original header that contained the entire email including an encoded version of the png. All together the header contents were 59K. Isn't that a bit big for an SMTP header?
This should be fixed by https://git.sr.ht/~sircmpwn/aerc/commit/2559ebfac56a8060c8af001ba61709f3c4d78d04