Earlier quoted context omitted.
> E-Mail before we lost the "text should be text and not goddamn HTML" war. It didn't work. To this day, if you begin a plain text email message with the word "From", you'll confuse mail programs because there wasn't a proper encoding of the body of the message separate from the headers.
> To this day, if you begin a plain text email message with the word "From", you'll confuse mail programs […] RFC 5322: > […] The body is simply a sequence of > characters that follows the header section and is separated from the > header section by an empty line (i.e., a line with nothing preceding > the CRLF). What brain dead mail program interprets anything after the first empty line as a header?
Some that I used that I remember such problems with include the MUA inside Netscape Navigator and mutt.