Unblock a spam user account in Office 365

I had a client who couldn’t send emails anymore. When he emailed someone he received a bounce back error saying “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.


  1. Ask the user to change their password or reset their password via the 365 admin portal. Their account password could have been hacked and therefore it was sending out spam/virus emails.
  2. Login to the 365 admin portal
  3. Click on Security
  4. Click on Alerts, Dashboard and scroll down to Restricted Users.
  5. Find the user and click unblock.

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