How do I properly encode a mailto link?

Question

I am generating some HTML and I want to generate an XSS- and database-content-safe mailto link. What is the proper encoding to use here? How's this?

myLiteral.Text = string.Format(
  "mailto:{0}?Content-Type=text/html&Subject={1}&body={2}", 
  HttpUtility.UrlEncode(email_address),
  HttpUtility.UrlEncode(subject),
  HttpUtility.UrlEncode(body_message));

Should I use UrlEncode here? HtmlEncode? Do what I did, then HtmlEncode the entirety? I'm writing HTML of a URL, so I'm a little unclear...

@Quentin, is this what you're describing? (Changed &s to & since I'm about to HtmlEncode...)

myLiteral.Text = 
  HttpUtility.HtmlEncode(HttpUtility.UrlEncode(
    string.Format(
      "mailto:{0}?Content-Type=text/html&Subject={1}&body={2}", 
      email_address, subject, body_message)));

Answer 1

You are putting some content in a URL, then representing that URL in HTML. So URLEncode it then HTMLEncode what you get from URLEncode.