Is looks really all that counts to you? :)
s/looks/usability/ if you want. It's a mail client. It doesn't have to do much other than read and reply to mail. There are advanced niceties (GPG signing, etc) but By the way, there's currently no policy to (my knowledge) regarding HTML posting to the list. In general, "top posting" is the correct method to reply to a HTML email (it's defined in the RFC) and while some people don't like it, cat not withstanding, it hasn't really been abused. Would people like me to are look at if I can turn HTML posting off to the list?
Btw: Thunderbird is themeable, as is Mozilla..
Not to make it look "exactly" like a "native Windows application"; this is one of the requirements of having a cross platform app; it can't rely on native widgets and render the same on all platforms. Remember that if the similarities are major, the differences are even worse! Craig