Why can’t i send email

Question

I can’t send email, i have error code 550 5.1.8. Please help me

Answer 1

Dear Brown Jack,

Based on your description, I understand that one of your users is unable to send outbound emails and is receiving the following error: 550 5.1.8 Access denied, bad outbound sender AS(42004)

This error indicates that our Exchange Online Protection system has detected suspicious activity, such as sending spam, from this account. To protect your organization's reputation and the Microsoft 365 service, the account has been automatically blocked from sending email and placed on the Restricted Entities list in the Microsoft 365 Defender portal.

Before removing the block, it is essential to ensure the account is no longer compromised. Failure to secure the account first will likely result in it being blocked again. Please ensure that the following actions have been taken for the affected user account: reset the password and enable Multi-Factor Authentication (MFA).

Then, unblock the Account from the Restricted Entities List. Once the account has been secured, a Global Administrator or Security Administrator can remove the sending block by following these steps:

• Go to the Microsoft 365 Defender Portal > Email & collaboration > Review > Restricted entities.
• If the account is there, the admin must remove it from restriction after verifying security.

Note: After you unblock the account, it should be able to resume sending emails within an hour. If the underlying cause of the compromise is not addressed, the account may be automatically restricted again.

Additionally, only a user with administrator permissions (such as a Global Admin or Security Admin) can access the Restricted Entities page in the Defender portal to remove the sending block. There is no self-service way to unblock your own account from this list.

For your reference, please refer to this official documentation: NDR error code "550 5.1.8 Access denied, bad outbound sender" - Microsoft Support

I appreciate your patience, and I am here to help. Looking forward to your response!

Thank you very much for your valuable time and your cooperation.