The Emacs MIME library will respect the use-hard-newlines
variable (see Hard and Soft Newlines in Emacs Manual) when encoding a message, and the
“format=flowed” Content-Type parameter when decoding a message.
On encoding text, regardless of use-hard-newlines, lines
terminated by soft newline characters are filled together and wrapped
after the column decided by fill-flowed-encode-column.
Quotation marks (matching ‘^>* ?’) are respected. The variable
controls how the text will look in a client that does not support
flowed text, the default is to wrap after 66 characters. If hard
newline characters are not present in the buffer, no flow encoding
occurs.
You can customize the value of the mml-enable-flowed variable
to enable or disable the flowed encoding usage when newline
characters are present in the buffer.
On decoding flowed text, lines with soft newline characters are filled
together and wrapped after the column decided by
fill-flowed-display-column. The default is to wrap after
fill-column.
mm-fill-flowed ¶If non-nil a format=flowed article will be displayed flowed.