SO won't let me add a comment... using the -M "text/html" option generates an error: s-nail: Only one of -M, -m or -q may be given s-nail (s-nail v14.9.22): send and receive Internet mail

I specify -M, -r, -s and multiple -a options, and for the input use a "heredoc" that contains the html code.

I don't know why it's complaining about "only one of -M, -m or -q" when that's what I have...