Martin Tournoij has written an article about line breaks in emails. Some people think that in text emails, lines should not be longer than ~78 characters. I also find that emails that have been adjusted to this limit look terrible on the smartphone because the maximum width is narrower than 78 characters.
It seems to me that “hard-wrap all text at 78 characters” is a misreading of the standard and a confusion between “how things should be sent on the wire” and “how things should be displayed”.
And a bit of criticism of the people who insist on wrapping lines in emails can also be found in the article:
“Educating” an entire population on how to do it “correct” because they’re all “wrong” seems not just like a fool’s errand, but also rather arrogant. You’re essentially just saying everyone should adjust to your personal preferences. Meh.
Martin’s solution (which I also prefer):
So these days I just write paragraphs on a single line, which will look great for everyone unless you’re not soft-wrapping the text, but that is a choice you’re making yourself.