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 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.
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 | Microsoft Access project extension |
.adp | Microsoft Access project |
.app | FoxPro generated application |
.bas | Microsoft Visual Basic class module |
.bat | Batch file |
.chm | Compiled HTML Help file |
.cmd | Microsoft Windows NT command script |
.com | Microsoft MS-DOS program |
.cpl | Control Panel extension |
.crt | Security certificate |
.csh | Unix shell script |
.exe | Executable file or program |
.fxp | Microsoft FoxPro file |
.hlp | Help file |
.hta | HTML program |
.inf | Setup information |
.ins | Internet naming service |
.isp | Internet communication settings |
.js | Jscript file |
.jse | Jscript-encoded script file |
.ksh | Unix shell script |
.lnk | Shortcut |
.mda | Microsoft Access add-in program |
.mdb | Microsoft Access program |
.mde | Microsoft Access MDE database |
.mdt | Microsoft Access file |
.mdw | Microsoft Access file |
.mdz | Microsoft Access wizard program |
.msc | Microsoft Common Console document |
.msi | Windows Installer package |
.msp | Windows Installer patch |
.mst | Visual Test source files |
.ops | FoxPro file |
.pcd | Photo CD image or Microsoft Visual Test compiled script |
.pif | Shortcut to MS-DOS program |
.prf | Microsoft Outlook Profile Settings |
.prg | FoxPro program source file |
.reg | Registration entries |
.scf | Windows Explorer Command file |
.scr | Screen saver |
.sct | Windows script component |
.shb | Shortcut into a document |
.shs | Shell scrap object |
.url | Internet shortcut |
.vb | VBScript file |
.vbe | VBScript-encoded script file |
.vbs | VBScript file |
.wsc | Windows script component |
.wsf | Windows script file |
.wsh | Windows script host settings file |
.xsl | XML file that can contain script |
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” earlier in this chapter.