Unable to Send Emails

Question

I am currently unable to send emails from my account. Whenever I try to send an email, I receive the following delivery failure message:

"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."

The diagnostic information includes the following error:

550 5.1.8 Access denied, bad outbound sender AS(42004)

Could you please investigate this issue and help restore my email sending capability? It appears that my account may have been flagged or blocked from sending outbound messages.

Please let me know if you need any additional information from my side.

Answer 1

Hi HO SSD Department  

May I kindly confirm whether you have already contacted your IT administrator within your organization?

My recommendation is to reach out to the person or team who provided you with this account, as they are in the best position to review and handle this situation more thoroughly. 

Please note that we are not Microsoft support, and this is a user-to-user support forum. Moderators and contributors, including external Microsoft employees, do not have backend access and cannot directly intervene in Microsoft products or features. Our role is limited to providing technical guidance and best practice recommendations based on reported issues, requests, or ideas.   

Once you connect with your administrator, you may refer them to the following article for more details: Remove blocked users from the Restricted entities page - Microsoft Defender for Office 365 | Micros… 

Only administrators have the required permissions to verify this and remove the restriction by going to the Microsoft Defender portal: https://security.microsoft.com, go to Email & collaboration > Review > Restricted entities. Or they can go directly using this link:  https://security.microsoft.com/restrictedentities. 

 

I hope this helps clarify the situation. 

---

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 2

how to check the activity of mail. I want to know who had accessed or what mails were sent from the mail address

Answer 3

I understand that my account was restricted due to suspected spam activity after it was compromised. I have already changed my password and taken steps to secure the account.

Could you please advise me on the recovery process and let me know what additional actions are required to restore full access and email sending functionality for my account?

I would appreciate any guidance you can provide regarding the next steps.

Answer 4

I would like to inform you that my email account was recently compromised. Someone gained unauthorized access to my account and sent multiple emails without my knowledge.

As soon as I became aware of the issue, I immediately changed my password and updated all related account credentials to secure the account. Since then, I have not noticed any further suspicious activity.

However, after changing the password, I have been unable to send emails from my account. I continue to receive the error message indicating that my account is blocked from sending outbound emails.

Could you please review the status of my account and remove any restrictions if the account is now considered secure? I would appreciate your assistance in restoring my email sending privileges.

Answer 5

The error 550 5.1.8 Access denied, bad outbound sender indicates that the account has been blocked from sending mail because it exceeded Exchange Online sending limits or was suspected of sending spam.

Resolution depends on the role:

1. For the mailbox user

• Check whether the account is compromised by following the guidance in determine whether your account is compromised.
• If there are any signs of compromise (unexpected sign-ins, rules, or forwarding), change the password and follow the remediation steps provided there.
• Inform the email administrator that the account is likely blocked for outbound spam.

2. For the 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 revoke any suspicious sessions.
4. Unblock the user
   • 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, restrictions are typically removed within about an hour and normal sending should resume.
5. Prevent future issues
   • Review and apply the recommendations in Top 10 ways to secure your business data, such as enabling multi-factor authentication and monitoring for suspicious activity.

If the account is consumer Outlook.com rather than an organization mailbox, and this is a new account, also be aware that low sending quotas can apply until sufficient reputation is built, as described in Sending limits in Outlook.com.

---

References:

• NDR error code "550 5.1.8 Access denied, bad outbound sender"
• Can't send or receive email in Outlook.com
• Sender Support in Outlook.com