[ale] Mail client that allows editing of source of HTML mail before sending?

[jb at sourceillustrated.com (John Wells)]

Guys,

I'm looking for a gui email client that allows editing of HTML source
before sending an email.  In other words, I can edit the mail WYSIWYG,
click "Edit source" or something similar, and then add a few lines of raw
HTML.

Anyone know of one out there that allows this?  Evolution does not, as far
as I can tell.

Thanks!
John