Users in your organization might get blocked from sending emails in Microsoft 365 if they exceed one of the outbound sending limits or inbound spam policies.

If a user is added to the restricted user list, they will receive the following NDR when trying to send emails out of the organization.

“Your message couldn’t be delivered because you weren’t recognized as a valid sender. The most common reason for this is that your email address is suspected of sending spam and it’s no longer allowed to send email. Contact your email admin for assistance. Remote Server returned ‘550 5.1.8 Access denied, bad outbound sender.”

Admins in your organization can remove users from the restricted users list, this can be done either via the Microsoft Defender 365 portal or via PowerShell.

To remove the user from the restricted list in the Microsoft Defender 365 Portal

  1. Open the Microsoft 365 Defender portal
  2. Go to Email & Collaboration > Review > Restricted users.
  1. Click on Restricted user page
  1. On the restricted users page, you will see a list of users who are blocked from sending emails from your organization.
  2. Review the user you would like to unblock, Select the user, and then click on Unblock.
  1. Once you click on Unblock a page with actions will open, here you have an option to Enable MFA for the users.
  2. When you’re finished with the actions and recommendations for the user, click on Submit.
  3. Click YES to confirm the change.

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