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Office 365 (Outlook on the Web) - Blocked File Attachment Types

Outlook on the Web by default blocks the attachment file types listed below.

The following document types may be blocked from being opened in Outlook Web App.  A possible workaround is to use the Outlook desktop user (either on Mac or Windows) to download these blocked attachments. Please use caution when attempting to open a file attachment from an unexpected source.  

Extension File Type
.asp Active Server Page
.aspx Active Server Page Extended
.apk Android Package File
.ani Animated Mouse Cursors
.ace Archive File Format
.arj arj compressed file
.bas BASIC Source Code
.bat Batch Processing
.cab Cabinet archive file
.crt Certificate File
.com Command
.chm Compiled HTML Help
.xz Compressed archive
.z Compressed archive
.csh csh Script
.dex Dalvik executable format
.lha Data compression file format
.lzh Data compression file format
.deb Debian package format
.der DER Encoded X509 Certificate File
.plg Developer Studio Build Log
.sys Device driver file
.vxd Device driver file
.cer Digital Certificate
.crt Digital Certificate
.der Digital Certificate
.img Disk images
.iso Disk images
.cmd DOS CP/M Command File, Command File for Windows NT
.dll Dynamic link library
.elf Executable and linkable format
.app Executable Application
.exe Executable File
.xml Extensible Markup Language
.fxp FoxPro Compiled Source (Microsoft)
.hta Hypertext Application
.inf Information or Setup File
.its Internet Document Set, Internet Translation
.url Internet Location
.cer Internet Security Certificate File
.jar Java File
.jnlp - Java File
.js JavaScript Source Code
.jse JScript Encoded Script File
.lib Linker input file
.macho Mach object file format
.kext macOS drivers
.mau Media Attachment Unit
.mhtml -   MIME Html
.prg Program File
.py Python File
.pyc Python File
.pyo Python File
.pyw Python File
.pyz Python File
.pyzw Python File
.rev RAR Recovery volume set
.reg Registration Information/Key for W95/98, Registry Data File
.shs Shell Scrap Object File
.tmp Temporary File/Folder
.appcontent-ms Third-party Application
.cnt Third-party Application
.diagcab Third-party Application
.grp Third-party Application
.hpj Third-party Application
.mcf Third-party Application
.msu Third-party Application
.pl Third-party Application
.printerexport Third-party Application
.settingcontent-ms Third-party Application
.theme Third-party Application
.uif Third-party Application
.vbp Third-party Application
.webpnp Third-party Application
.website Third-party Application
.xbap Third-party Application
.xll Third-party Application
.xnk Third-party Application
.ksh UNIX Shell Script
.vbe VBScript Encoded Script File
.vb VBScript File or Any Visual Basic Source
.vbs VBSript Script File, Visual Basic for Applications Script
.vst Virtual Studio Technology
.msix Windows app package 
.scf Windows Explorer Command
.hlp Windows Help File
.msi Windows Installer File
.msp Windows Installer Update 
.cdxml Windows PowerShell
.ps1 Windows PowerShell
.ps1xml  Windows PowerShell
.ps2   Windows PowerShell
.ps2xml  Windows PowerShell
.psc1  Windows PowerShell
.psc2  Windows PowerShell
.psd1  Windows PowerShell
.psdm1  Windows PowerShell
.pssc  Windows PowerShell
.scr Windows Screen Saver
.wsc Windows Script Component
.ws Windows Script File
.wsf Windows Script File
.wsh Windows Script Host Settings File
.mst Windows SDK Setup Transform Script
.lnk Windows Shortcut File
.shb Windows Shortcut into a Document
.prf Windows System File
.gadget Windows Vista Gadget
.library -  Third-party Application
  
Microsoft Extensions File Type
.maf Access 
.mda Access Add-in , MDA Access 2 Workgroup 
.mdt Access Add-in Data 
.mdb Access Application , MDB Access Database 
.maw Access Data Access Page 
.mag Access Diagram Shortcut 
.mam Access Macro Shortcut 
.mde Access MDE Database File 
.mad Access Module Shortcut 
.adp Access Project 
.ade Access Project Extension 
.maq Access Query Shortcut 
.mar Access Report Shortcut 
.mas Access Stored Procedures 
.mat Access Table Shortcut 
.mav-  Access View Shortcut 
.mdz Access Wizard Template 
.mdw Access Workgroup Information 
.ins IIS Internet Communications Settings 
.isp IIS Internet Service Provider Settings 
.appx Microsoft AppX Application Package
.appref-ms Microsoft Component
.udl Microsoft Component
.wsb Microsoft Component
.msc Microsoft Management Console Snap-in Control File  
.msh Microsoft Shell
.msh1 Microsoft Shell
.msh1xml Microsoft Shell
.msh2 Microsoft Shell
.msh2xml Microsoft Shell
.mshxml Microsoft Shell
.docm Microsoft Word Macro Enabled Document
.pst MS Exchange Address Book File, Outlook Personal Folder File 
.ops Office Profile Settings File
.ppa PowerPoint add-in
.ppam PowerPoint add-in
.vss Visio Stencil
.vsw Visio Workspace File 
.vsmacros Visual Studio .NET Binary-based Macro Project 
.pcd-   Visual Test 
.cpl Windows Control Panel Extension 
.pif Windows Program Information File 
.sct Windows Script Component, Foxpro Screen