Sylpheed is a simple, lightweight but full-featured, and easy-to-use e-mail client (mailer, MUA).

Features:

• Simple, beautiful, and well-polished user interface
• Comfortable operationality which is built in detail
• Immediately available with minimal configuration
• Lightweight operation
• High reliability
• Internationalization and Multilingualization support
• High-level Japanese processing
• Various protocols support
• Security features (GnuPG, POP3/IMAP4/NNTP over SSL/TLSv1)
• Powerful filtering
• Junk mail control
• Flexible cooperation with external commands

Linux, BSD, and Mac OS X versions available.

What's New in version 2.6.0 RC:

• The backups for configuration files are kept for four generations now.
• Only new messages are counted when incorporating from local mbox.
• In the folder selection dialog, only folders which are expanded in the folder view are expanded now.
• The folders which should not be selected in the folder selection dialog became unselectable now.
• The bug that the addressbook window was not refreshed when sender of message was added to the addressbook was fixed.
• The compilation error in GTK+ 2.14.x was fixed.
• Several bugfixes were made.
• Win32: The Japanese manual was updated.