I use Gmail as my mail client, but not really using the @gmail.com address, rather with my personal and university address. Now I was wondering why there isn't an alternative that offers similar functionality (ie. good client and great spam filter). Maybe I just don't know it, but I take it that it cannot be very famous then...
I was just thinking about this being a great startup idea. You could immediately make it a paid product, argumenting that you solve the privacy concerns many (especially here) have.
