Blocked from sending work emails

Question

I cannot send emails from work account I get the following:

Delivery has failed to these recipients or groups:

[Moderator note: Personally Identifiable Information removed] This message couldn't be delivered because the sending email address was not recognized as a valid sender. The most common reason for this error is that the email address is, or was, suspected of sending spam. Contact the organization's email admin for help and give them this error message.

Answer 1

Hi Tom,

Good day. Thank you for reaching out, and I appreciate you sharing the details of your situation. 

Just a quick note before we continue: this is a user-to-user community forum, so I don’t have access to your Microsoft 365 tenant, your account, or your device to make changes directly. However, I’m here to support you the best I can within these constraints, by providing clear next steps, sharing applicable resources, and directing you to the appropriate support channels.  

Based on the error message you received, it appears that your work email account is currently being restricted by Microsoft 365 from sending outbound emails. The sending email address is being marked as not recognized as a valid sender. 

This commonly happens when an account has been flagged due to possible spam activity, excessive outbound email sending, or unusual sign-in/sending behavior. In some cases, this can also indicate that the account may have been compromised. 

In this case, your organization’s IT Administrator will need to review the account in Microsoft 365 Admin Center or Microsoft Defender and remove the sending restriction if appropriate. 

Please reach out to your internal IT/Admin team and share the information below with them for further investigation. 

They may check the following: 

1/ Check Restricted Entities in Microsoft Defender 

• Go to: https://security.microsoft.com 
• Navigate to Email & collaboration 
• Select Review > Restricted entities 
• Search for the affected user account 
• If the account is listed, select the user and choose Unblock 

Reference: Remove blocked users from the Restricted entities page - Microsoft Defender for Office 365 | Micros… 

2/ Run a Message Trace in Exchange Admin Center 

• Go to: https://admin.exchange.microsoft.com 
• Navigate to Mail flow > Message trace 
• Click Start a trace 
• Enter the affected sender and recipient email address 
• Select the date and time range when the failed email was sent 
• Click Search 
• Review the trace results to check whether the message was failed, rejected, deferred, or delivered 
• Open the failed message and review the failure reason, delivery status, and any related error details 

Reference: Message trace in the new EAC in Exchange Online | Microsoft Learn 

3/ Review account security 

• Check recent sign-in activity for suspicious logins 
• Reset the user’s password if needed 
• Enable or verify Multi-Factor Authentication 
• Review any suspicious inbox rules, forwarding rules, or delegated access 

4/ Check outbound spam policies 

• Confirm whether the account was blocked due to outbound spam detection 
• Review any alerts in Microsoft Defender or Microsoft 365 Admin Center 

Once the account has been reviewed and unblocked, it may take some time for mail sending to resume normally. 

Additionally, if needed, your IT team can also raise a support ticket with Microsoft Support through the Microsoft 365 Admin Center for deeper investigation. They have access to backend configurations and can perform a more in-depth investigation. At the very least, they can provide the most effective workaround to ensure your experience remains smooth and secure.      

In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support  

I hope this information is helpful. Should you have any further questions or need additional assistance, please feel free to share them in the comment below. I'm very happy to help.  

---

If the answer is helpful, please click "Accept Answer" and kindly upvote it.

Note: Follow the steps in our documentation to enable email notifications if you want to receive email notifications related to this topic.

Answer 2

The error indicates the account has been blocked as a bad outbound sender, typically because it exceeded Exchange Online sending limits or was suspected of sending spam.

Resolution depends on role:

For the user (work account owner)

1. Check whether the account might be compromised (unexpected sent items, unusual sign-ins, or rules forwarding mail). Use the guidance in determine whether your account is compromised.
2. Inform the organization’s email administrator and provide the full Non-Delivery Report (NDR), including the error text.

For the email administrator

1. Follow the steps to secure a compromised email account in Exchange Online if compromise is suspected: Secure a compromised email account in Exchange Online.
2. Go to the Microsoft 365 Defender portal → Restricted entities page (https://security.microsoft.com/restrictedusers).
3. Locate the blocked user account and unblock it.
4. After unblocking, allow up to about an hour for restrictions to be removed so the user can send email again.
5. Review and apply the recommendations in Top 10 ways to secure your business data to reduce the chance of future blocks.

This error will continue until the admin removes the restriction on the account.

---

References:

• NDR error code "550 5.1.8 Access denied, bad outbound sender"