Sylpheed is an e-mail client (and news reader) based on GTK+ 2, running on
X Window System, and aiming for:
  * Quick response
  * Graceful, and sophisticated interface
  * Easy configuration, intuitive operation
  * Abundant features

Currently, many features are supported including POP3, IMAP, NNTP,
multiple accounts, threading, filtering, MIME attachments, APOP, SMTP
AUTH, SSL, IPv6, GnuPG, internalization, and more.

WWW: http://sylpheed.sraoss.jp/en/