Opera 10.0 - Free Email Browser, Now Lets You Send Emails Rich as Web Pages

Opera, the now data-compressing browser is also an email program, of course — now rich-text-sending.
Next to HTML email composition, Opera 10 brings spell-checking as you type, lots of small refinements and the option to delete mail from POP servers for a few days after downloading:
›› The Opera email client is a slick and flexible interface that will satisfy almost all your email needs, and Opera integrates RSS feeds in this experience as well. (Windows)