Sending mail: line wrapping and quoted-printable encoding

[Radu Butoi]

Hello all,

I've recently set up my mail in Emacs, and it works well. Gmail, though,
doesn't support [1] format=flowed, resulting in the hard-to-read comb
effect when viewing on mobile, which I'd like to avoid. Doing some more
research, I see that the quoted-printable encoding (which Gmail does
support [2], and I've confirmed) can also be used to avoid hard line
breaks while keeping under the line length limit.

Now, I'd like to configure Emacs to send mail using this encoding. To
test this I overwrite `sendmail-program` to log what Emacs sends.
Reading the message-mode and Emacs MIME manuals, I tried setting the
following variables:

(setq
 mm-content-transfer-encoding-defaults
 '((".*" quoted-printable))
 mm-body-charset-encoding-alist
 '((iso-8859-1 . quoted-printable)
   (utf-8      . quoted-printable))
 mm-use-ultra-safe-encoding t)

When sending, no encoding to quoted-printable is done (and there's no
Content-Transfer-Encoding header). To try to debug this further,
inserted the following into a buffer and ran M-: (mml-to-mime)

test test test <...longer than 78 columns...>

And there is still no encoding header or wrapping with =. Does anyone
know what is going on here?

More generally, since I'm new to terminal-based email, what is the
etiquette around hard-wrapping (or not)? Would it be rude to send
paragraphs as one logical line (wrapped-in-transmission by
quoted-printable) and expect people to soft-wrap?

Thanks in advance,
Radu

[1]: https://useplaintext.email/, and many blog posts mentioning the
same. It seems like Gmail used to support this, from the screenshot in
https://github.com/legoscia/messages-are-flowing.

[2]: https://mathiasbynens.be/notes/gmail-plain-text