Pegasus Mail founder and developer, David Harris has killed off the freeware E-mail client due to a lack of funds. 

It has been around since 1990, originally developed for MS-DOS, but soon gained popularity within Windows, Apple and Novell Netware environments. Many features which are now commonplace in today's E-mail clients, such as multiple POP3 access, were pioneered by Harris in Pegasus Mail.
On his website, Harris states: "Effective January 2007, development and distribution of Pegasus Mail and Mercury has ceased. We regret this decision, but ongoing difficulties with funding have forced it upon us.
"Sites who have current support subscriptions will be fully supported until their subscriptions expire. We will be looking at developing migration tools to assist those sites in moving to other platforms or products."
But there could be a dim glimmer of light at the end of the tunnel for current users.
In a later addendum, Harris says: "I stress that this is purely a decision brought on by financial difficulty: if sponsors could be found to provide modest ongoing funding, I would be happy to continue developing the programs, and would even consider opening the source."