Changes to Outlook on the web blocked file extensions and MIME types in Exchange Server 2019 and 2016

Applies to: Exchange Server 2019Exchange Server 2016


For Microsoft Exchange Server 2019 and Exchange Server 2016, the following type of file extensions and Multipurpose Internet Mail Extensions (MIME) in Outlook on the web (formerly known as Outlook Web App) are restricted to sending:
  • .appref-ms - Windows ClickOnce
  • .cdxml - PowerShell cmdlet definition
  • .pssc - PowerShell session configuration
  • .udl - Microsoft Data Link, used by Microsoft Data Access Components (MDAC)
  • .wsb - Windows sandbox
  • .vhd
  • .vhdx
  • .py
  • .pyc
  • .pyo
  • .pyw
  • .pyz
  • .pyzw

How to get this update

To get this update, install one of the following updates:

For Exchange Server 2019, install the Cumulative Update 6 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.​

For Exchange Server 2016, install the Cumulative Update 17 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.


Learn about the terminology that Microsoft uses to describe software updates.