Mozilla Thunderbird is a free, cross-platform e-mail and news client developed by the Mozilla Foundation. The project strategy is modeled after Mozilla Firefox, a project aimed at creating a web browser. Just as Firefox aims to redefine the web browser, Thunderbird is a refinement of the mail and news interface. On December 7, 2004, version 1.0 was released, and received over 500,000 downloads in its first three days of release (and 1,000,000 in 10 days). As of 2007, Thunderbird has been downloaded more than 50 million times since 1.0 release.
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Microsoft Outlook or Outlook (full name Microsoft Office Outlook since Outlook 2003) is a personal information manager from Microsoft, and is part of the Microsoft Office suite.

Although often used mainly as an e-mail application, it also provides a calendar, task and contact management, note taking, a journal and web browsing.

It can be used as a stand-alone application, but can also operate in conjunction with Microsoft Exchange Server to provide enhanced functions for multiple users in an organization, such as shared mailboxes and calendars, public folders and meeting time allocation.
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Eudora is an e-mail client used on the Apple Macintosh and Microsoft Windows operating systems. It also supports several palmtop computing platforms, including Newton and the Palm OS. The software was named after Eudora Welty because of her short story "Why I Live at the P.O." Eudora was developed by Steve Dorner in 1988 who worked at the Computer Services Organization of the University of Illinois at Urbana-Champaign. Eudora was acquired by Qualcomm in 1991. In 2006 Qualcomm stopped development of the commercial version, and sponsored the creation of a new open-source version based on Mozilla Thunderbird code-named Penelope.
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