If your organization requires that users be able to download attachment of these types from OWA, you should first ensure that our organization's operating systems and application software are up-to-date (in the case files that are opened by application software) or ensure that your users are familiar with the risks associated with the file types (in the case of files that are interpreted by scripting software). However, if your users are sending and receiving affected attachments, they will report that they are no longer able to download them. The newly blocked file types are rarely used, so most organizations will not be affected by the change. We’re always evaluating ways to improve security for our customers, and so we took the time to audit the existing blocked file list and update it to better reflect the file types we see as risks today. This change will prevent Outlook on the web users from downloading attachments that have those file extensions. We will soon be adding several additional file extensions to the BlockedFileTypes property of existing OwaMailboxPolicy objects.

March 6, 2020: We will also be blocking.May 2, 2022: We will also be blocking .application.

How to view file types in the name