Fix Microsoft 365 User Still Blocked from Sending Email After Unblocking
Question details
A Microsoft 365 mailbox remains unable to send emails even after an administrator has removed the user from the Restricted users list.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- A user tries to send outbound emails after being recently unblocked in the Microsoft 365 Defender portal, but the emails still fail to send and generate bounce-backs.
- Observed behavior
- Outbound emails are continuously blocked, generating a Non-Delivery Report (NDR) indicating the user is restricted due to spam policies or recipient-volume thresholds.
Ensure you have administrator access to the Microsoft 365 Defender portal and have a copy of the latest Non-Delivery Report (NDR) bounce-back message for analysis.
Wait for System Sync and Verify the Unblock Status
Removing a user from the Restricted users list is not always instantaneous; it takes time for the service-side block to fully clear across all servers.
When an admin removes a user from the Restricted users portal, the action updates backend databases. This update must propagate across Microsoft's global server infrastructure before the outbound sending restriction is completely lifted.
Navigate to the Microsoft 365 Defender portal and sign in with your global administrator or security administrator credentials.
Go to 'Email & collaboration' in the left menu, select 'Review', and then click on 'Restricted users'.
Verify that the affected user's account is no longer listed on this page.
Allow up to 24 hours from the exact time of unblocking for the Microsoft 365 backend services to fully process the change and lift the restriction.
Analyze the NDR and Adjust Sending Practices
Repeatedly hitting spam or volume thresholds will result in the user being immediately blocked again by automated systems.
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Frequently Asked Questions
Why is my Microsoft 365 account blocked from sending emails?
Accounts are automatically blocked by Microsoft's anti-spam controls when they exceed outbound sending limits, such as the recipient-volume threshold, or exhibit suspicious email activity resembling spam.
How long does it take to send emails again after being unblocked in Microsoft 365 Defender?
After an administrator removes an account from the Restricted users portal, it can take up to 24 hours for the backend changes to propagate globally and the sending block to be fully lifted.
Can I use standard Microsoft 365 mailboxes for sending mass marketing emails?
No, standard Microsoft 365 mailboxes are not designed for bulk mailing. Using them for mass marketing frequently triggers outbound sending restrictions. It is highly recommended to use a dedicated bulk-mailing platform instead.
