Bonus, xclip can be directed provide the rich text directly to the clipboard (op this might offer you a solution that is usable as text by your recipients):

`cat something.md | pandoc -f gfm -t html | xclip -selection clipboard -t text/html`

other output type targets also available, check xclip docs

my small experience with Wayland suggested this sort of thing might be more difficult there, but dunno