Send & Receive Issues

How to Fix Cannot Send Email Access Denied Error 550 5.1.8

Maira Mehtab Sep 22, 2026 869 views

Question details

Users are unable to send emails and receive an access-denied message indicating a bad outbound sender.

Product: Microsoft 365 Email
Device & OS: not provided
Scenario: Attempting to send an outbound email message to any recipient.
Observed behavior: The email fails to send and returns a non-delivery report (NDR) containing an access-denied message and SMTP error code 550 5.1.8.

Before you start

Keep the full non-delivery report (bounce-back message) in your inbox, as your IT administrator will need the exact error codes to diagnose and resolve the issue.

Solution 1Recommended

Contact Your Microsoft 365 Global Administrator

This error requires administrative privileges to fix, as it indicates the account has been blocked from sending emails due to suspected outbound spam activity.

SMTP error 550 5.1.8 means that your Microsoft 365 account has triggered automated security alerts and has been restricted from sending outbound messages. As an end-user, you cannot remove this restriction yourself.

Retrieve the full NDR

Open the bounce-back email you received and copy the entire text, making sure to include the exact error code 550 5.1.8.

Reach out to IT support

Contact your organization's IT department or Microsoft 365 global administrator and provide them with the complete non-delivery report.

Request restriction review

Ask the administrator to log into the Microsoft 365 Defender portal to review your account's sender and outbound-spam restrictions and unblock the account.

Open a Microsoft service request

If the administrator is unable to unblock the account manually, they will need to open a formal service request with Microsoft 365 Support on your behalf.

For Reseller Customers: If your organization purchased Microsoft 365 through a third-party reseller, your internal administrator may need to contact the reseller directly to lift the outbound sending block.

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Frequently Asked Questions

What does SMTP error 550 5.1.8 mean?

This specific error code indicates that your email address has been flagged for sending spam or suspicious bulk emails, resulting in the server blocking your ability to send outbound messages.

Can I fix the 550 5.1.8 access denied error by myself?

No, end-users cannot lift this restriction. You must contact your Microsoft 365 global administrator or IT department, as only they have the necessary permissions to unblock the account.

What is a non-delivery report (NDR)?

An NDR is an automated bounce-back email generated by the mail server when a message cannot be delivered. It contains diagnostic information and error codes that are essential for IT support to troubleshoot the failure.

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