Email Attachments blocked by Microsoft Outlook – the new and complete list

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Here’s a complete, searchable and sortable list of all the email attachments that are or soon will be blocked by various types of Microsoft Outlook.

There’s confusion and inconsistencies in the Microsoft documentation and application of these new blocks.

They have a list of blocked attachments for Outlook in  “Office 365,, Outlook 2019 Outlook 2016, Outlook 2013, Outlook 2010, Outlook 2007”.  No mention of Office for Mac so we’re hoping that Office 365 and 2019 for Mac are included.

That’s blocking by software only. These days most anti-spam and virus checks are done by the mail service not the software on your computer.

There’s the list of extra extensions that will soon be blocked by ‘Outlook on the web’ (aka Outlook Web Access OWA).  This really means Exchange hosted by Microsoft as part of Office 365 hosting.

Administrators can unblock any of these extensions or add more to the blocked list.

No word on how this affects Outlook.com but it’s likely the same extensions will also be blocked on Microsoft’s free email service.

Outlook for Windows

October patches for Outlook for Windows include updates which will block Python related extensions (.py, .pyc, .pyo, .pyw, .pyz & .pyzw).

No mention of the other files newly blocked by Microsoft’s online services.

The patches are:

Outlook 2016 for Windows  KB4484107

Outlook 2013 for Windows  KB4484096

Outlook 2010 for Windows  KB4475604

Rarely Used?

According to Microsoft  “The newly blocked file types are rarely used, so most organizations will not be affected by the change. “

That’s mostly true, however the new list includes the main Windows PowerShell script .ps1 which Microsoft uses itself to automate administration and setup tasks.  They are hardly ‘rarely used’ and network administrators will be vexed if .ps1 extensions are blocked in emails.

Sundries = Microsoft

Many of the newly blocked extensions are lumped together as “… used by various applications”.  They don’t mention that 14 of these 17 ‘other’ troublesome extensions where made and distributed by Microsoft!

All these are courtesy of Microsoft: .appcontent-ms, .settingcontent-ms, .cnt, .website, .webpnp, .printerexport, .theme, .vbp, .xbap, .xll, .xnk, .msu, .diagcab, .grp

Only these three came from non-Microsoft sources: .hpj, .pl,.mcf

Email Attachments block list

We’ve merged Microsoft various lists into a single table.  The listed attachments are or soon will be blocked by Microsoft mail services.

Sort: click on the headings.  Search: enter text in box at right.

ExtensionNew in late 2019?Name
.mafAccess (Microsoft)
.mdaAccess Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdtAccess Add-in Data (Microsoft)
.mdbAccess Application (Microsoft), MDB Access Database (Microsoft)
.mawAccess Data Access Page (Microsoft)
.magAccess Diagram Shortcut (Microsoft)
.mamAccess Macro Shortcut (Microsoft)
.mdeAccess MDE Database File (Microsoft)
.madAccess Module Shortcut (Microsoft)
.adpAccess Project (Microsoft)
.adeAccess Project Extension (Microsoft)
.maqAccess Query Shortcut (Microsoft)
.marAccess Report Shortcut (Microsoft)
.masAccess Stored Procedures (Microsoft)
.matAccess Table Shortcut (Microsoft)
.mavAccess View Shortcut (Microsoft)
.mdzAccess Wizard Template (Microsoft)
.mdwAccess Workgroup Information (Microsoft)
.aspActive Server Page
.hpjNEWAppWizard Help project WinHelp / RoboHelp
.basBASIC Source Code
.batBatch Processing
.derNEWCertificate - DER Encoded X509 Certificate File
.cerNEWCertificate - Internet Security Certificate File
.crtNEWCertificate File
.comCommand
.chmCompiled HTML Help
.cshcsh Script
.plgDeveloper Studio Build Log
.cmdDOS CP/M Command File, Command File for Windows NT
.xllNEWExcel add-in
.xnkNEWExchange / Outlook Public Folder Shortcut
.appExecutable Application
.exeExecutable File
.fxpFoxPro Compiled Source (Microsoft)
.htaHypertext Application
.insIIS Internet Communications Settings (Microsoft)
.ispIIS Internet Service Provider Settings (Microsoft)
.infInformation or Setup File
.itsInternet Document Set, Internet Translation
.websiteNEWInternet Explorer Pinned site shortcut
.urlInternet Location
.jarNewJava Archive
.jnlpNewJava Network Launch Protocol
.jsJavaScript Source Code
.jseJScript Encoded Script File
.mauMedia Attachment Unit
.udlNEWMicrosoft Data Access Components (MDAC)
.cntMicrosoft Help Workshop Application
.mscMicrosoft Management Console Snap-in Control File (Microsoft)
.grpNEWMicrosoft program group
.mshMicrosoft Shell
.msh1Microsoft Shell
.msh1xmlMicrosoft Shell
.msh2Microsoft Shell
.msh2xmlMicrosoft Shell
.mshxmlMicrosoft Shell
.diagcabNEWMicrosoft Support diagnostic tools
.pstMS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.opsOffice Profile Settings File
.osdOpen Software Description 
.plNEWPerl script
.prgProgram File
.pyNEWPython
.pycNEWPython
.pyoNEWPython
.pywNEWPython
.pyzNEWPython
.pyzwNEWPython
.regRegistration Information/Key for W95/98, Registry Data File
.shsShell Scrap Object File
.tmpTemporary File/Folder
.kshUNIX Shell Script
.mcfNEWVarious: Media Container Format (most likely) but could be a rare printer package or Norton Security History.
.vbeVBScript Encoded Script File
.vbVBScript File or Any Visual Basic Source
.vbsVBScript Script File, Visual Basic for Applications Script
.vswVisio Workspace File (Microsoft)
.vbpNEWVisual Basic project file
.vsmacrosVisual Studio .NET Binary-based Macro Project (Microsoft)
.pcdVisual Test (Microsoft)
.appcontent-msNEWWindows app content information
.appref-msNEWWindows ClickOnce
.cplWindows Control Panel Extension (Microsoft)
.themeNEWWindows desktop themes
.scfWindows Explorer Command
.cntNEWWindows Help
.hlpWindows Help File
.msiWindows Installer File (Microsoft)
.mspWindows Installer Update
.ps1NEWWindows PowerShell
.ps1xmlNEWWindows PowerShell
.ps2NEWWindows PowerShell
.ps2xmlNEWWindows PowerShell
.psc1NEWWindows PowerShell
.psc2NEWWindows PowerShell
.psd1NEWWindows PowerShell
.psdm1NEWWindows PowerShell
.xbapNEWWindows Presentation Foundation – XAML
.printerexportNEWWindows Printer backup file
.webpnpNEWWindows Printer package
.pifWindows Program Information File (Microsoft)
.wsbNEWWindows Sandbox
.scrWindows Screen Saver
.wscWindows Script Component
.sctWindows Script Component, Foxpro Screen (Microsoft)
.wsWindows Script File
.wsfWindows Script File
.wshWindows Script Host Settings File
.mstWindows SDK Setup Transform Script
.settingcontent-msNEWWindows Settings shortcut
.lnkWindows Shortcut File
.shbWindows Shortcut into a Document
.prfWindows System File
.msuNEWWindows Update
.gadgetWindows Vista gadget

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