Postmaster is a GUI based email client for the BeOS platform. In the event that Postmaster receives an email containing a URL consisting of over 512 bytes, the application will crash when attempting to create a link within the body of the message. Postmaster will continue to crash upon restart until the offending email is manually removed from /boot/home/mail/in/.
This issue was rectified with the release of Postmaster version 1.1.1. It is available for download at the following location: http://kennyc.com/postmaster/download.html