Attachment File Types Restricted by Outlook 2003

By default, access is restricted to certain e-mail message attachments in Microsoft® Outlook®. In determining which attachments are blocked, Outlook checks the file type of the attachment. Files with certain file types can be completely blocked (Level 1) or the user may be required to save a file to disk before opening the file (Level 2).

By default, Outlook classifies a number of file type extensions as Level 1 and blocks files with those extensions from being received by the users. There are no Level 2 file types by default, but you can create a list of Level 2 file types by using the Outlook Security template. You can demote file types from being categorized as Level 1 to being Level 2, or you can add other file types to create a Level 2 list.

 Note   To learn more about why some attachments are blocked, see Blocked attachments: The Outlook feature you love to hate. In addition, users can find methods for sharing files that are blocked by Outlook by reading About unblocking attachments.

Level 1 file types blocked by Outlook

The following table lists the Level 1 file types that are blocked under a default installation of Microsoft Office Outlook 2003. You can add or remove items from the default list through the Outlook Security Settings tab of the Outlook Security template.

File extension File type
.ade Access Project Extension (Microsoft)
.adp Access Project (Microsoft)
.app Executable Application
.asp Active Server Page
.bas BASIC Source Code
.bat Batch Processing
.cer Internet Security Certificate File
.chm Compiled HTML Help
.cmd DOS CP/M Command File, Command File for Windows NT
.com Command
.cpl Windows Control Panel Extension (Microsoft)
.crt Certificate File
.csh csh Script
.exe Executable File
.fxp FoxPro Compiled Source (Microsoft)
.hlp Windows Help File
.hta Hypertext Application
.inf Information or Setup File
.ins IIS Internet Communications Settings (Microsoft)
.isp IIS Internet Service Provider Settings (Microsoft)
.its Internet Document Set, Internation Translation
.js JavaScript Source Code
.jse JScript Encoded Script File
.ksh UNIX Shell Script
.lnk Windows Shortcut File
.mad Access Module Shortcut (Microsoft)
.maf Access (Microsoft)
.mag Access Diagram Shortcut (Microsoft)
.mam Access Macro Shortcut (Microsoft)
.maq Access Query Shortcut (Microsoft)
.mar Access Report Shortcut (Microsoft)
.mas Access Stored Procedures (Microsoft)
.mat Access Table Shortcut (Microsoft)
.mau Media Attachment Unit
.mav Access View Shortcut (Microsoft)
.maw Access Data Access Page (Microsoft)
.mda Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdb Access Application (Microsoft), MDB Access Database (Microsoft)
.mde Access MDE Database File (Microsoft)
.mdt Access Add-in Data (Microsoft)
.mdw Access Workgroup Information (Microsoft)
.mdz Access Wizard Template (Microsoft)
.msc Microsoft Management Console Snap-in Control File (Microsoft)
.msi Windows Installer File (Microsoft)
.msp Windows Installer Patch
.mst Windows SDK Setup Transform Script
.ops Office Profile Settings File
.pcd Visual Test (Microsoft)
.pif Windows Program Information File (Microsoft)
.prf Windows System File
.prg Program File
.pst MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.reg Registration Information/Key for W95/98, Registry Data File
.scf Windows Explorer Command
.scr Windows Screen Saver
.sct Windows Script Component, Foxpro Screen (Microsoft)
.shb Windows Shortcut into a Document
.shs Shell Scrap Object File
.tmp Temporary File/Folder
.url Internet Location
.vb VBScript File or Any VisualBasic Source
.vbe VBScript Encoded Script File
.vbs VBScript Script File, Visual Basic for Applications Script
.vsmacros Visual Studio .NET Binary-based Macro Project (Microsoft)
.vss Visio Stencil (Microsoft)
.vst Visio Template (Microsoft)
.vsw Visio Workspace File (Microsoft)
.ws Windows Script File
.wsc Windows Script Component
.wsf Windows Script File
.wsh Windows Script Host Settings File

The following table lists the Level 1 file types that are blocked under a default installation of Microsoft Office Outlook 2003 Service Pack 3 (SP3).

File extension File type
.der DER Encoded X509 Certificate File
.gadget Windows Vista Gadget
.msh Microsoft Shell
.mshxml Microsoft Shell
.msh1 Microsoft Shell
.msh1xml Microsoft Shell
.msh2 Microsoft Shell
.msh2xml Microsoft Shell
.plg Developer Studio Build Log
.ps1 Windows PowerShell
.ps1xml Windows PowerShell
.ps2 Windows PowerShell
.ps2xml Windows PowerShell
.psc1 Windows PowerShell
.psc2 Windows PowerShell
.xnk Exchange Public Folder Shortcut

Level 2 file types restricted by Outlook

There are no Level 2 file types by default, but you can create a list of Level 2 file types for your deployment. Level 2 file types are restricted (under a default installation of Outlook 2003) and you must first save a Level 2 file to disk before you can open it —Level 2 file types cannot be opened directly from an item in an e-mail message.

As an administrator, you can add or remove attachment types from the list of Level 2 file types through the Outlook Security Settings tab of the Outlook Security form. Also, you can demote attachment file types from Level 1 to Level 2 by using the Level1Remove registry key. For more information about setting the Level1Remove registry key, see Administrator-Controlled Settings vs. User-Controlled Settings.