UPDATED ON: December 8, 2010
For safety reasons Koma-Mail blocks scripts and ActiveX in your mails. You can also encrypt your user account. To be protected against webbugs you can use Koma-Mail in the offline mode.
Koma-Mail offers two different spam filters: one is word based and the other one is a Bayesian. To prevent false negative detections Koma-Mail uses a white list.
With Koma-Mail you can send and receive mails, encrypted via SSL, through POP3, IMAP (including synchronization), SMTP and WebDav. To stay informed you can use the integrated RSS viewer.
Altogether Koma-Mail is a good alternative to shareware mail clients.