PHP
(a quick example)
MAIL TO + MAIL SUBJECT $to = "jon@doe.com"; $subject = "Test";
MAIL MESSAGE $body = "<html><body> <strong>HTML 強い</strong> </body></html>";
MAIL HEADER $head = implode("\r\n", [ "MIME-Version: 1.0", "Content-type: text/html; charset=utf-8" ]);
SEND MAIL mail ($to, $subject, $body, $head);
Yes, we can inline CSS <p style="font-weight:bold">BLAH<>/p>. But <style> tags will probably not work in many mail clients.