This page presents some of the most used email clients available in gNewSense.
More on the Claws-Mail's official website.
Note: When composing a message, you may have the following error:
Error Spell checker could not be started. No word lists can be found for the language "en_US".
For this error to disappear, you have to disable Spell checking in claws-mail: Configuration -> Preferences -> Compose -> Spell Checking (many thanks to http://ubuntuforums.org/archive/index.php/t-469783.html).
More on the Emacs' official website.
Mutt is a command-line email client.
Note: thunderbird has been found to suggest non-free addons, but this issue has been worked on in gNewSense, so you should'nt have this problem in the future.