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Microsoft Outlook Express

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Microsoft Outlook Express

This article is about the Windows component. For the personal information manager included in the Microsoft Office suite, see Microsoft Outlook.
Outlook Express
A component of Microsoft Windows
Windows XP
Type Email client, News client
Included with Windows 98, Windows Me, Windows 2000, Windows XP, Windows Server 2003
Also available for Mac OS 9, Windows 3.x, Windows NT 3.51, Windows 95, Windows NT 4.0
Replaces Microsoft Internet Mail and News
Replaced by Windows Mail
Related components
Internet Explorer

Outlook Express is an email and news client that is included with Internet Explorer versions 4.0 through 6.0. As such, it is also bundled with several 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 In Windows Vista, Outlook Express was superseded by Windows Mail, then again by Windows Live Mail as separate software. Microsoft Outlook (previously Microsoft Entourage), sold as part of Microsoft Office for Macintosh, has replaced the Macintosh version.

Outlook Express is a different application from Microsoft Outlook. The two programs do not share a common codebase, but do share a common architectural philosophy. The similar names lead many people to conclude incorrectly that Outlook Express is a stripped-down version of Microsoft 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.


Microsoft Internet Mail and News was a email and news client and ancestor of Outlook Express. Version 1.0 was released in 1996 following the Internet Explorer 3 release.[1] This add-on precedes the Internet Mail profile for Microsoft Exchange 4.0 bundled in Windows 95. Version 2.0 was released at the end of 1996. In 1997 the program was changed and renamed as Outlook Express and bundled with Internet Explorer 4. The executable file for Outlook Express, msimn.exe, is a holdover from the Internet Mail and News era. Internet Mail and News handled only plain text and rich text (RTF) email, lacking HTML email.

At one point, in a later beta version of Outlook Express 5, Outlook Express contained a sophisticated and adaptive spam filtering system; however this feature was removed shortly before launch. It was speculated on various websites and newsgroups at that time, that the feature was not stable enough for the mass market. Nearly two years later, a similar system, using a similar method of adaptive filtering, appeared as a feature of Microsoft Outlook.

Internet Explorer 5 required Outlook Express 5 to save Web Archive files (see MHTML).[2]

In October 2005, Microsoft announced that Windows Vista would exclusively include a new application named Windows Mail, based on large parts of Outlook Express source code.[3] In November 2007, Microsoft released Windows Live Mail (originally Windows Live Mail Desktop), a mail client for its Hotmail service.

Versions for Windows

  • Outlook Express 4.0, which was included in Windows 98 (June 1998), stored messages in *.mbx files (similar to the Mbox format used in Unix based systems).
  • Outlook Express 5.0, which was included in Windows 98 Second Edition (SE) (June 1999), switched to *.dbx files, with a separate file for each mailbox folder.
  • Outlook Express 5.01 was included in Windows 2000 (February 2000).
  • Outlook Express 5.5 was included in Windows Me (June 2000).
  • Outlook Express 6.0 was included in Windows XP (October 2001).

Version for Mac


Email standards

Beginning with the text-based Unix Mail command, e-mail traditionally used the inline or bottom posting styles when replying to messages. Outlook Express, as well as Lotus Notes and Microsoft Outlook, top-post (show replies newest to oldest) by default. The large installed base of Microsoft Windows and Microsoft Office has changed perceptions of posting style to the point where new users have come to expect the top-posting style and are confused by inline or bottom posting.

Microsoft Outlook and Microsoft Exchange use a proprietary e-mail attachment format called Transport Neutral Encapsulation Format (TNEF) to handle formatting and other features specific to Outlook such as meeting requests. Outlook Express and other e-mail clients are unable to read this format.[4] This can be confusing to Outlook Express users (as well as those who use other e-mail clients) who receive attachments sent from Outlook.

Database corruption

Outlook Express has been prone to a number of problems which can corrupt its files database, especially when the database increases in size due to an increasing number of stored emails and during database compaction. This has led to a thriving market for programs that can back up, restore and recover corrupted files.[5] An open-source project called UnDBX was also created, which seems to be successful in recovering corrupt databases. Microsoft has also released documentation[6] which may be able to correct some non-severe problems and restore access to e-mail messages, without resorting to third-party solutions.

However, with the latest updates applied, Outlook Express now makes backup copies of DBX files prior to compaction. They are stored in the Recycle Bin. If an error occurs during compaction and messages are lost, the DBX files can be copied from the recycle bin.

Security issues

Outlook Express was one of the earlier e-mail clients to support HTML e-mail and scripts. As a result, emails were commonly infected with viruses. Previously, another security flaw was that a script could automatically be opened as an attachment. Another bug was in Outlook Express's attachment handling that allowed an executable to appear to be a harmless attachment such as a graphics file. Opening or previewing the e-mail could cause code to run without the user's knowledge or consent. Outlook Express uses Internet Explorer to render HTML e-mail. Internet Explorer has been widely criticized[weasel words] for having numerous security flaws.

With Outlook Express SP2 (part of Windows XP SP2), Microsoft has tried to correct the security holes. Outlook Express now blocks images inside e-mails by default.[7][8] It uses only the restricted security zone for HTML e-mail, which disables scripts and imposes restrictions on what web content can be rendered. It also warns when opening potentially malicious attachments.[9]

Handling of PGP/MIME signed messages

Outlook Express does not correctly handle MIME,[10] and will not display the body of signed messages inline. Users get a filled e-mail and one attachment (one of the message text and one of the signature) and therefore need to open an attachment to see the e-mail. If the email has been forwarded several times, users need to open attached email messages one inside the other multiple times to reach the parent e-mail message. This bug has still not been rectified. The proper behavior is described in RFC1847.[11] When replying or forwarding a message to a user who has a digital signature, Outlook Express gives an error and does not allow the user to continue if there is no digital signature installed for the sender.[12]


Outlook Express does not have a documented object model like Microsoft Outlook. Programmatic access to, or control of Outlook Express for custom messaging applications or plugins is not officially documented and supported by Microsoft.[13] IStoreNamespace and IStoreFolder interfaces[14] were documented in 2003, but they are only related to the storage.

Some companies have managed to create their plugins hacking the interface using Windows hooks. A significant one was the PGP plugin because it was the only example of a working plugin whose source code was available (licensed under GPL). By 2003, some companies provided commercial solutions to develop add-ins.[15]

Office 2007 spell checker incompatibility

Outlook Express does not have a dedicated spell checker. It can use the spell checkers from Microsoft Office if Office is also installed. However, the Office 2007 spell checkers, except for the French spell checker, are incompatible with Outlook Express. Microsoft has acknowledged this problem,[16] but does not provide any sort of remedy. A solution is to install any pre-Office 2007 proofing tools or use a third party spell checking program for Outlook Express. Windows Live Mail, which is based on Outlook Express's source code, contains built-in spell checking support (now for US English and numerous other languages) and is freely downloadable for Windows XP.

Glitches and other unusual aspects

Cancelling sending an email while it is being sent does not effectively prevent it from being sent.[17] Also, when importing .PST files, cancelling the import while it is in progress merely cancels the import of the current folder and the import resumes with the next folder. Also, .pst file size used for "received" or "sent" folders is limited to 2Gb. After that non-describing error occurs.

See also


External links

  • Differences between Outlook and Outlook Express, from the Microsoft knowledge base
  • Outlook Express Help - Tips and Tricks How to use Outlook Express, setup and configure new email accounts including Gmail, backup emails, message rules, email signatures etc.
  • Secunia commercial security firm compares the latest unpatched known flaws of Outlook Express with those of other e-mail clients
  • Outlook Express API article article giving an introduction about how to use some of the Outlook Express API.
  • Outlook Express dbx file format by Arne Schloh - a partial documentation of the DBX file format with sample code
  • Outlook Express 5.0 file format - another reverse-engineered .dbx document with sample code
  • Outlook Express Video Setup - Kurulum - Outlook Express Video Setup - Kurulum
  • Outlook 2003 Setup - Kurulum - Outlook 2003 Video Setup
  • UnDBX - an open-source tool to extract, recover and undelete e-mail messages from Outlook Express DBX files.
  • [1]
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