Last month, I decided to drop Evolution and start using claws-mail. Now that I've been using it everyday, I see that it fits very well my needs as a mail user agent.

I will list the features I like in Claws-Mail, instead of writing a huge boring paragraph:

• Tree view (or Thread view) for emails that are related (replies for examples)
• GPG support through plugins (MIME or inline, and with SHA512 support too!)
• Very lightweight (almost all of the time less than 10mb ram used)
• Can display HTML emails in plain text (by stripping the html) and it works really good
• Rules/Actions can be added for a lot of events
• Bogofilter spam filter support through plugins
• HTML viewer, just in case! (added through plugin)
• Choose which headers to show when reading email (see screenshot: I chose to show the SPF header)
• "Next" button to quickly read the next unread email
• Extract email addresses from received mails and add them into your addressbook.
• Different Layouts, even one for small screens
• Many other features...

Claws-Mail is well worth the try, there are lots of nice features like those. And I'm quite happy to have switched to it.

You can either find claws-mail through your package management system (synaptic, yum, rpm, ...) or through the official website.
I also packaged it for Ubuntu/Debian without the maemo support for LPIA architecture (this was for my HP mini 1000).