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.

Extension	New in late 2019?	Name
.maf		Access (Microsoft)
.mda		Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdt		Access Add-in Data (Microsoft)
.mdb		Access Application (Microsoft), MDB Access Database (Microsoft)
.maw		Access Data Access Page (Microsoft)
.mag		Access Diagram Shortcut (Microsoft)
.mam		Access Macro Shortcut (Microsoft)
.mde		Access MDE Database File (Microsoft)
.mad		Access Module Shortcut (Microsoft)
.adp		Access Project (Microsoft)
.ade		Access Project Extension (Microsoft)
.maq		Access Query Shortcut (Microsoft)
.mar		Access Report Shortcut (Microsoft)
.mas		Access Stored Procedures (Microsoft)
.mat		Access Table Shortcut (Microsoft)
.mav		Access View Shortcut (Microsoft)
.mdz		Access Wizard Template (Microsoft)
.mdw		Access Workgroup Information (Microsoft)
.asp		Active Server Page
.hpj	NEW	AppWizard Help project WinHelp / RoboHelp
.bas		BASIC Source Code
.bat		Batch Processing
.der	NEW	Certificate - DER Encoded X509 Certificate File
.cer	NEW	Certificate - Internet Security Certificate File
.crt	NEW	Certificate File
.com		Command
.chm		Compiled HTML Help
.csh		csh Script
.plg		Developer Studio Build Log
.cmd		DOS CP/M Command File, Command File for Windows NT
.xll	NEW	Excel add-in
.xnk	NEW	Exchange / Outlook Public Folder Shortcut
.app		Executable Application
.exe		Executable File
.fxp		FoxPro Compiled Source (Microsoft)
.hta		Hypertext Application
.ins		IIS Internet Communications Settings (Microsoft)
.isp		IIS Internet Service Provider Settings (Microsoft)
.inf		Information or Setup File
.its		Internet Document Set, Internet Translation
.website	NEW	Internet Explorer Pinned site shortcut
.url		Internet Location
.jar	New	Java Archive
.jnlp	New	Java Network Launch Protocol
.js		JavaScript Source Code
.jse		JScript Encoded Script File
.mau		Media Attachment Unit
.udl	NEW	Microsoft Data Access Components (MDAC)
.cnt		Microsoft Help Workshop Application
.msc		Microsoft Management Console Snap-in Control File (Microsoft)
.grp	NEW	Microsoft program group
.msh		Microsoft Shell
.msh1		Microsoft Shell
.msh1xml		Microsoft Shell
.msh2		Microsoft Shell
.msh2xml		Microsoft Shell
.mshxml		Microsoft Shell
.diagcab	NEW	Microsoft Support diagnostic tools
.pst		MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.ops		Office Profile Settings File
.osd		Open Software Description
.pl	NEW	Perl script
.prg		Program File
.py	NEW	Python
.pyc	NEW	Python
.pyo	NEW	Python
.pyw	NEW	Python
.pyz	NEW	Python
.pyzw	NEW	Python
.reg		Registration Information/Key for W95/98, Registry Data File
.shs		Shell Scrap Object File
.tmp		Temporary File/Folder
.ksh		UNIX Shell Script
.mcf	NEW	Various: Media Container Format (most likely) but could be a rare printer package or Norton Security History.
.vbe		VBScript Encoded Script File
.vb		VBScript File or Any Visual Basic Source
.vbs		VBScript Script File, Visual Basic for Applications Script
.vsw		Visio Workspace File (Microsoft)
.vbp	NEW	Visual Basic project file
.vsmacros		Visual Studio .NET Binary-based Macro Project (Microsoft)
.pcd		Visual Test (Microsoft)
.appcontent-ms	NEW	Windows app content information
.appref-ms	NEW	Windows ClickOnce
.cpl		Windows Control Panel Extension (Microsoft)
.theme	NEW	Windows desktop themes
.scf		Windows Explorer Command
.cnt	NEW	Windows Help
.hlp		Windows Help File
.msi		Windows Installer File (Microsoft)
.msp		Windows Installer Update
.ps1	NEW	Windows PowerShell
.ps1xml	NEW	Windows PowerShell
.ps2	NEW	Windows PowerShell
.ps2xml	NEW	Windows PowerShell
.psc1	NEW	Windows PowerShell
.psc2	NEW	Windows PowerShell
.psd1	NEW	Windows PowerShell
.psdm1	NEW	Windows PowerShell
.xbap	NEW	Windows Presentation Foundation – XAML
.printerexport	NEW	Windows Printer backup file
.webpnp	NEW	Windows Printer package
.pif		Windows Program Information File (Microsoft)
.wsb	NEW	Windows Sandbox
.scr		Windows Screen Saver
.wsc		Windows Script Component
.sct		Windows Script Component, Foxpro Screen (Microsoft)
.ws		Windows Script File
.wsf		Windows Script File
.wsh		Windows Script Host Settings File
.mst		Windows SDK Setup Transform Script
.settingcontent-ms	NEW	Windows Settings shortcut
.lnk		Windows Shortcut File
.shb		Windows Shortcut into a Document
.prf		Windows System File
.msu	NEW	Windows Update
.gadget		Windows Vista gadget