cant forward emails each get error code

Hi @Mack SAMUEL,

If forwarding is blocked by organization policy, the error message usually includes 550 5.7.520 access denied. But based on your sharing, this error message means that your mailbox has been restricted from sending because it is flagged for suspected outbound spam and is highly on the Restricted entities list in Microsoft Defender.

For the best approach to resolve this issue, please contact your administrator to check whether your mailbox is blocked in Restricted entities folder. Please note that this action requires admin privileges so contact you IT help desk to ask for assistance if you are an end-user. You can look for the way to find your admin through this link: How do I find my Microsoft 365 admin? - Microsoft Support.

• Go to Microsoft Defender portal > Email & Collaboration > Review > Restricted Entities
• If your mailbox is listed, select and choose Unblock then wait within 1 hour (occasionally up to 24 hours) until restrictions are removed from your account.
• For reference, you can share your admin the details from this article so they can help remove restrictions for your account Remove blocked users from the Restricted entities page - Microsoft Defender for Office 365 | Microsoft Learn

Please understand that my initial response does not always resolve the issue immediately. However, you can try these steps and let me know if it works for you. If not, we can work together to find a solution.

If you have any questions or need further assistance, please feel free to share them in the comments on this post so I can continue to support you.    

Thank you for your understanding and cooperation. I'm looking forward to your reply.

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The error indicates that the sender has been blocked as a “bad outbound sender” because the account is suspected of sending spam or has exceeded Exchange Online sending limits. As long as the account remains blocked, any attempt to send or forward mail will fail with this type of message.

Resolution depends on the role:

1. For the affected user

• Stop trying to resend or forward from the blocked account until it is cleared.
• Check whether the account might be compromised (unexpected sent items, inbox rules, or sign-ins). See the guidance in “determine whether your account is compromised,” then report the issue to the organization’s email administrator.

2. For the Microsoft 365 email administrator
3. Secure the account
   • Follow the steps in “Secure a compromised email account in Exchange Online” to:
     • Reset the user’s password.
     • Remove any malicious inbox rules or forwarding.
     • Review sign-in activity and take any additional remediation steps.
4. Unblock the sender
   • Go to the Microsoft 365 Defender portal → Restricted entities page (https://security.microsoft.com/restrictedusers).
   • Locate the affected user account and remove it from the restricted list.
   • After unblocking, allow up to about an hour for restrictions to clear so the user can send/forward mail again.
5. Prevent future issues
   • Review and apply the recommendations in “Top 10 ways to secure your business data” to reduce the risk of future compromise and outbound spam.

If the environment is not administered directly (for example, hosted by another organization or provider), contact that organization’s email admin and provide the full error text so they can perform the unblock and security checks.

References:

• NDR error code "550 5.1.8 Access denied, bad outbound sender"
• Email nondelivery reports and SMTP errors in Exchange Online