I came here to comment about this. Rainloop is amazing.

It also has some extra security features for the end user. For instance, you can tell Rainloop to proxy images from the email and serve them to you instead of your browser getting them from a remote source. It's amazing because you get faster load times and don't leak your desktop IP, only whatever server your running Rainloop on.

The only thing it's lacking is PGP, which is very sad.