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

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.