Outlook Express is an email and news client that is integrated with Internet Explorer versions 4.0 through 6.0. It is also bundled with a number of versions of Microsoft Windows, from Windows 98 to Windows Server 2003, and is available for Windows 3.x, Windows NT 3.51, Windows 95 and Mac OS 9. In Windows Vista, Outlook Express was outdated by Windows Mail, then again by Windows Live Mail as separate software in Windows 7. Microsoft Entourage, sold as part of Microsoft Office for Macintosh, has changed the Macintosh version. Outlook Express is a diverse application from Microsoft Office Outlook. The two programs do not share a common codebase, but do share a common architectural philosophy. The similar names lead many people to incorrectly conclusion that Outlook Express is a stripped-down version of Microsoft Office Outlook. Outlook Express utilizes the Windows Address Book to store contact information and incorporates tightly with it. On Windows XP, it also joins together with Windows Messenger.