Balsa – open source E-mail client for GNOME
Balsa is a lightweight, easy to use open-source E-mail client for GNOME, highly configurable and incorporating all the features you would expect in a robust mail client.

It’s a Gnome e-mail client that supports multiple POP3 and IMAP accounts and local mail delivery. Balsa can be compiled with multi-threading support for faster response and can do nifty things like read your GnomeCard address book, use LDAP, and render HTML mail.
It has a spell checker and direct support for PGP and GPG for encryption and also has some necessary filtering capabilities, and natively supports several e-mail storage protocols. It also has some internationalization support, including Japanese fonts.
Features of Balsa – E-mail client for GNOME
- Support for local mailbox formats: Mbox, Maildir, mh
- Allows nested mailboxes
- Support for POP3 and IMAP mail access protocols
- Printing
- Spell Checking
- Multi-threaded mail retrieval (Optional Feature)
- MIME support (view images inline, save parts)
- Supports for SMTP and use of local MTA, ie. Sendmail
- Address Book that integrates with GnomeCard
- Highly configurable
- Active, open development
- Multiple character sets for composing and reading messages
- Allows file attachments to outgoing messages
- GPG/OpenPGP mail signing and encryption
- Website: http://balsa.gnome.org/index.html
- Download: http://balsa.gnome.org/download.html