MS Outlook Express – A Guide to Origin, History and Replacement

admin | December 19th, 2016 | Technology

In the vast domain of email clients, there will be a name that will always be remembered for its HTML emails and scripts. Outlook Express a widely used email client in its time, was introduced with Internet Explore from version 4.0 to version 6.0. It was also a part of some versions of Windows OS like Windows 98 to Windows 2003, Windows 3.xWindows NT 3.51Windows 95, and Mac OS 9. MS Outlook Express replaced Microsoft Internet Mailand News.

Due to the similarities in their names, MS Outlook and Outlook Express are often considered as related to each other. In fact, Outlook Express is said to be the descendant of MS Outlook. However, this is not true. It is completely a different application from MS Outlook and holds no similarity except common architectural philosophy.

History of Outlook Express

The origin of Outlook Express is marked by Microsoft Internet Mail and News. It was email and news client introduced in the year 1996 as a part of Internet Explorer version 3. In 1997, the program was renamed as Outlook Express with Internet Explorer version 4.0. The executable file of Microsoft Internet Mail and News, i.e. msimn.exe was handed down to Outlook Express as the executable file. In the later times, with the release of beta version of Outlook Express version 5, an advanced spam filter was introduced in it. However, because of the criticism faced by it due to its instability for mass market, the feature was removed soon before being launched.

The database of Outlook Express 4.0 was MBOX format. The emails were stored in .mbx file. However, in Outlook Express 5.0, this database format changed to .dbx files. For each default folder of Outlook Express, a separate DBX file is created.

Versions of Outlook Express




Operating System








Windows 98

Microsoft 98 For Macintosh



June, 1998





Windows 98 Second Edition


June 1999





Windows 2000


February 2000





Windows Me


June 2000





Windows XP


October 2001

Issues with Outlook Express

  • Difference In Email Standards

One of the issues faced by Outlook Express users was the incompatibility of email standards of OE with other email clients. For instance, MS Outlook and MS Exchange deploy a Transport Neutral Encapsulation format for its attachments. This format is not decoded or supported by Outlook Express and thus its users are not able to understand the attachments sent form such email clients.

  • Corruption Issues

The main reason behind corruption in Outlook Express is issues in its database due to exceed in its size limit. The maximum limit of the size of DBX files is 2 GB. In case the database size increases, the database gets corrupted and hence leads to abrupt functioning of Outlook Express.

  • Issues In Security

Being one of the earliest email clients to use HTML scripts, the emails in Outlook Express were usually infected with virus. Another issue that was usually encountered with the email client was that any script used to get open as an attachment.

Replacementof Outlook Express

Eventually, Outlook Express was supervened upon by Windows Mail and after a period of time by Windows Live Mail in the form of different software for Windows operating system.

In Macintosh operating system, OE was superseded by Entourage up to 2008 edition. After that, Macintosh was replaced by MS Outlook 2011.