I am a happy user of the daily build of Thunderbird 3. Although it is still under development, is the best email client for Linux I’ve tried so far, at least, the one that better works for me. Email search & filtering is fast and reliable.
The only thing I don’t like is that wrapping your emails to 72 characters when sending plain text is not straightforward. Once you have selected to send your emails as plain text and have set the line wrap option to 72, there is still one more option to tweak.
Thunderbird has a “feature” that sends by default all plain text with the option format=flowed, which unwraps the email in the client receiver. To turn this feature off, you have to toggle one of the options in the chrome editor:
To disable flowed paragraphs, enforcing line breaks as formatted in the message, set the preference:
To disable paragraph flow when you send plain text messages, and in the plain text part of multipart messages, set the preference:
I put it here, in case is helpful to someone else.