Here's a nice simple trick.  If you don't like the way emacs is
formatting your text, one solution is to use an external program
to do it via "shell-command-on-region":

I was just writing a line of text with some embedded right angle
brackets in it: '>>'. The line was getting long but there's a bug with
M-q ("fill-paragraph") in emacs (at least in MH-Letter-mode).  It takes
a line like this:

  Right, that's probably a harder one: '>>' looks like it's part of a heredoc.

And wraps it like:

  Right, that's probably a harder one: '>>' looks like it's part of a
                                        >>heredoc.

Apparently it gets confused and thinks the angles indicate text quoted
from a previous reply...  The way I want this to wrap is like so:

  Right, that's probably a harder one: '>>' looks like it's part of
  a heredoc.

And that is exactly what this does (but you do need to select the text
first, before doing a "M-oM-f"):

  (defun doom-run-text-autoformat-on-region (start end)
    "Format the region using Text::Autoformat."
    (interactive "r")
    (let ( (command
            (format
               "perl -MText::Autoformat -e'autoformat {right=> %d, all=>1}'"
               fill-column)) )
      (shell-command-on-region start end command nil t "*error*")
      ))
  (global-set-key "\M-o\M-f" 'doom-run-text-autoformat-on-region)