What Is Freeware?
What is freeware? — Freeware is software developed created by volunteers, and distributed for free. Most of the time, freeware is developed by a single programmer.
Freeware email clients include Mozilla Mail, Mozilla Thunderbird, Opera Mail (Opera M2), Outlook Express, Apple Mail. (Although the only way to get Outlook Express Windows or Apple Mail is to purchase Microsoft Windows or Mac OS X)
What Is Open Source Software?
Open Source is more than usual freeware. Open source is a movement whose base credo is that software should be developed for free. Open source programs are usually developed by scores of programmers scattered throughout the globe.
Open Source is responsible for such pieces of software as the Mozilla and FireFox browser, the Thunderbird and Mozilla Mail email clients, etc.
Open Source is called "open source" because the source code behind these applications is opened to access by anyone who wishes to contribute to the global effort.
The Open Source Initiative website: OpenSource.org 


Email Clients Tutorials
Free Email Tutorials