Reclaim your inbox and whatnot.

I've been using Thunderbird for some months now, and I have to say it's ok. I would expect some more speed, after all it's just a mail client, dealing with text mostly... However, it's free, there are a lot of useful extensions, and - pay attention to this - it's totally cross-platform. By totally I mean that you can store all your mail in a folder inside a FAT32 partition, and use the very same data from Linux or Windows, with no ugly desyncing.

Anyway, it's worth a try even if you just use one operating system. Even just to use something different than outlook.