Microsoft Exchange Server: is a messaging and collaborative software product developed by Microsoft. It is part of the Microsoft Servers line of server products and is widely used by enterprises using Microsoft infrastructure solutions. Exchange's major features consist of electronic mail, calendaring, contacts and tasks; support for mobile and web-based access to information; and support for data storage.

Outlook Express: is an e-mail/news client that was included with Internet Explorer versions Internet Explorer 4.0 through 6.0. As such, it was also bundled with several versions of Microsoft Windows, from Windows 98 to Windows XP, and was available for Windows 95 and Mac OS 9. In Windows Vista, Outlook Express is replaced with Windows Mail. Windows Live Mail has since been released as the successor to Outlook Express and Windows Mail. Microsoft Entourage, sold as part of Microsoft Office for Macintosh, has replaced the Macintosh version. Outlook Express is a different application from Microsoft Office Outlook. The two programs do not share a common code base, but do share a common architectural philosophy. The similar names lead many people to incorrectly conclude that Outlook Express is a stripped-down version of Microsoft Office Outlook. Outlook Express uses the Windows Address Book to store contact information and integrates tightly with it. On Windows XP, it also integrates with Windows Messenger.