Claws Mail is an email client aiming at being fast, easy-to-use and powerful. It is mostly desktop-independent, but tries to integrate with your desktop as best as possible. The Claws Mail developers try hard to keep it lightweight, so that it should be usable on low-end computers without much memory or CPU power.
You can install Claws Mail using the clawsmail ppa. To add the ppa and install Claws Mail open a terminal window (press Ctrl+Alt+T) and copy+paste the following lines:
sudo add-apt-repository ppa:claws-mail/ppa
sudo apt-get update
sudo apt-get install claws-mail
To start Claws Mail and type: claws-mail
Main features: Claws Mail sports almost everything a perfect email client needs. Mail retrieval over POP3, IMAP4, local mbox, over SSL; support for various authentication schemes. It has multiple accounts and mailboxes, powerful filtering and search functionality, import/export capabilities using a number of formats, support for GnuPG (digital signatures and encryption). It supports plugins, customisable toolbars, spell checking, a number of guards to prevent any data loss, per-folder preferences, and much more. A list of features can be found at www.claws-mail.org/features.php.
Claws Mail Homepage
There are extra plugins which are not included in the Claws Mail source package, to install these plugins copy+paste the following line:
sudo apt-get install claws-mail-extra-plugins