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.
