Solution for IT team
The MS365 tech team confirmed that the quarantine response was a false positive. Unfortunately, the MS365 team cannot fix this globally, so each impacted sender must implement the troubleshooting steps they provided. Your company's IT team can help with this.
The solution is to release the quarantined messages and add the sender's email address to the allowed list.
Table of contents:
How to release quarantined messages in Microsoft 365 Defender's quarantine interface
Select any affected messages that were Quarantined under Microsoft 365 Defender > Email and collaboration > Review > Quarantine (Note: Only take these steps for emails quarantined that are known trusted sources)
Click Release email
3. Check the box that says Submit the message to Microsoft to improve detection (false positive)
4. Click Send
If a recipient is using a personal Outlook email, please share the solution below in the “How to allow the sender’s email address for personal/private Outlook users” section below.
How to allow the sender's email address for personal/private Outlook users
Outlook desktop app
In the Home tab, switch Ribbon to show more options and click on the Junk
Select Junk E-mail Options
3. Navigate to the Safe-senders tab
4. Click the Add button
5. Enter the email address into the field and hit OK
6. Close the Junk E-mail options by hitting OK
Outlook web app
Click the settings (cog) icon in the top right corner
Scroll down and click the View All Outlook Settings
In the Mail tab, navigate to the Junk Email section
Click Add in the Safe senders and domains category
Enter the email address into the input field and hit Enter