Outlook Express

Outlook Express (formerly Microsoft Internet Mail and News) was an E-mail program bundled with Microsoft Windows starting with Windows 98. You could download it onto machines running Windows 3.x, Windows 95, Windows NT 3.51, and Windows NT 4.0. The product was included on Windows 98 up to Longhorn before being discontinued in favor of Windows Mail found in RTM Windows Vista and in some betas of Windows 7 (though it was purposely broke in later builds) before being reintroduced in Metro language form in Windows 8 and 10. Many people often confuse this with Microsoft Outlook, bundled with Microsoft Office and hence think Outlook Express is a stripped down version of Microsoft Outlook, however that is not the case as the programs don't share a common code base.

Microsoft Internet Mail and News (1.0)
Microsoft Internet Mail and News was released in 1996.

Microsoft Internet Mail and News (2.0)
Microsoft Internet Mail and News 2.0 was released later in 1996. The following year, its name was changed to Outlook Express.

Outlook Express 3.0
Outlook Express 3.0 was the first version to carry the Outlook Express branding instead of the Microsoft Internet Mail and News branding. This version was released in 1997.

Outlook Express 4.0
Outlook Express 4.0 was released in June of 1998 and was bundled with Windows 98.

Outlook Express 5.0
Outlook Express 5.0 was released in June of 1999 and was bundled with Windows 98 Second Edition.

Outlook Express 5.01
Outlook Express 5.01 was released in February of 2000 and bundled with Windows 2000.

Outlook Express 5.5
Outlook Express 5.5 was released in June of 2000 and bundled with Windows ME.

Outlook Express 6.0
Outlook Express 6.0 was released in 2001 and bundled with Windows XP

Outlook Express 7.0
Outlook Express 7.0 was seen in beta builds of Windows Longhorn (Vista), which would indicate that Windows Vista was to have Outlook in the final RTM build, however, in 2005 Outlook Express 7.0, along with the WinFS feature heavily needed for it were both scrapped and replaced with Windows Mail, which has a similar layout. You can find Windows Mail in Windows 7 betas, though in later betas, it was intentionally broken. Windows 7 got Windows Live Mail instead. Windows Mail should not be confused with the Windows Mail present on 8 and 10 systems.

Replacement
As stated above, Outlook 7.0 was scrapped from Windows Vista and replaced with Windows Mail. This was included in many Windows 7 preview builds, though in later builds, it was intentionally broken. This was replaced in the final RTM build with Windows Live Mail, also downloadable for Windows XP, Vista, 8, 8.1, and 10 machines. In Windows 8, 8.1, and 10, Microsoft reused the Windows Mail name for a metro language mail app. Had Microsoft continued with the outlook branding, then Windows 7 would've gotten Outlook Express 8, Windows 8 would've gotten Outlook Express 9, Windows 8.1 would've gotten Outlook Express 9.1, and Windows 10 would've shipped with Outlook Express 10.