If you're in mail composition mode, which it sounds like you are, forget the "view source" option people are telling you.
You want HTML, not the raw email message with MIME-encoded HTML.
Do This Instead: while composing the message, click Edit->Select All
and then click the Insert->HTML
menu option.
The window that opens is small, so resize it. Your HTML message will be there (minus headers and body tags). This is more useful to copy a message out as HTML.
Likewise, you can create your message in your favorite HTML editor and insert it using this feature.
Though the menu command is Insert->HTML
, it also allows you to edit the message as HTML as long as you select the text before you invoke Insert->HTML
.
I often use this when forwarding a message that was a poorly designed email newsletter, and I need to tweak a few things before forwarding it.