It's entirely possible to send mail as format=flowed plain text, so that messages will rewrap nicely on any screen. I do it all the time with Mutt, it's actually very easy.
https://news.ycombinator.com/item?id=20514314
> The suggestion to use `format=flowed` doesn’t help, as the standard is ill-supported: https://fastmail.blog/2016/12/17/format-flowed/ I’ve researched the issue far and wide and the only way to have responsive, nicely wrapped emails is using HTML.
https://cpbotha.net/2016/09/27/thunderbird-support-of-rfc-36...
> Update on 2019-07-16 The current GMail web-ui ignores format=flowed and renders such emails with hard linebreaks everywhere. Thank you Google for violating yet more email standards.
Most people I correspond with where I care about my mail looking "normal" to them seem to use Gmail (about 30-50%), then Apple Mail, Outlook or Thunderbird.
One long line sounds likely to make the problem for that person worse not better!
That was a while ago though. Clients may have changed.
I'd love to know if someone has put the time into cross-platform tests for this sort of thing.
The only thing I'm completely confident of at the moment is that multipart/mixed text+HTML works for every client.