How to turn off blocked feature in OWA (Outlook Web App)

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PROBLEM

When you receive a new message in OWA (Outlook Web App), in receive address field appears the bellow message:
"To help protect your privacy, some content in this message has been blocked. If you're sure this message is from a trusted sender and you want to re-enable the blocked features, click here."

CAUSE

By default, OWA will block some external content in HTML messages, such as pictures or sounds linked within the message. These links are hidden references (not the underlined kind that you click to activate) in the HTML source code to an external location on the Internet, such as a website. They are triggered when the message is opened or previewed, which prompts a download of the external content. While some legitimate senders do this to avoid sending large messages, junk email senders use this technique to verify your email address as a legitimate one. Once verified, you will be targeted directly with more spam. If content is blocked, you will see this message: To help protect your privacy, some content in this message has been blocked. If you're sure this message is from a trusted sender and you want to re-enable the blocked features, click here.

SOLUTION

To work around this issue, you must create a test message without the blocked types of files, then send the test message to Exchange Online mailbox

Important: If it is not blocked, then, to help protect your privacy and prevent from any attack, it’s recommended not to change your default Outlook Web App Mailbox Policies.

If it is blocked, to check your Outlook Web App Mailbox Policies and change it, you can proceed with the following steps:

  1. Install and Configure Windows PowerShell
  2. Run the following command:
                  
    a. Run Get-OwaMailboxPolicy and check the BlockedMimeTypes and AllowedMimeTypes

 

            b. Run Set-OwaMailboxpolicy to change the blocked and allowed file types:
 

3. Set-OwaMailboxPolicy -Identity OwaMailboxPolicy-Default -AllowedFileTypes ".pdf", ".doc" and click Enter

 

4. Run again Set-OwaMailboxPolicy and check AllowedFileTypes and you'll see that ".pdf", ".doc" are allow files

 

 For additional information, please refer to the following pages: