Can't send or receive email from my exchange account on any device.

Hi Matthew,

I completely understand how frustrating it is to be unable to send or receive emails on any of your devices. I know how important email is for your daily work.

First, could you please confirm if your organization is using Exchange On-Premises or Exchange Online (Microsoft 365)?

If you are using Exchange Online (Microsoft 365):
Based on the error message, it is highly likely that your account has been blocked by Microsoft's security filters. You will need to contact your IT Administrator and ask them to perform the following checks:

1. Check for Quarantine or Spam Flags: If your organization uses Microsoft Defender for Office 365, your email admin can check the Outbound Spam section in the Microsoft 365 Security & Compliance Center to see if your account has been flagged.

You can follow this article for full instructions: Use the Microsoft Defender portal to manage quarantined email messages

2. Check "Restricted entities": This is the most critical step for the specific error you are seeing. Your admin needs to check if your account is listed under the "Restricted entities" page in the Microsoft Defender portal.

You can follow this article for full instructions on how to unblock the account: Remove a user from the Restricted entities page in the Microsoft Defender portal

I hope this helps. If you have any questions, or if I misunderstood or was unclear about anything, feel free to reach out anytime.

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The error indicates the account has been blocked as a bad outbound sender because it exceeded Exchange Online sending limits or was suspected of sending spam. As a result, messages cannot be sent, and in many cases receiving may also be affected until the account is remediated and unblocked.

Steps depend on the role in the organization:

1. For the mailbox user
   1. Check whether the account has been compromised by reviewing recent sign-ins, devices, and any unusual sending activity, following the guidance in determine whether your account is compromised.
   2. Change the account password and ensure multi-factor authentication is enabled if available.
   3. Inform the email administrator that the account is blocked with an NDR mentioning “sending email address was not recognized as a valid sender” / “suspected of sending spam.”
2. For the email administrator
   1. Treat the account as potentially compromised and follow the steps in Secure a compromised email account in Exchange Online to:
      • Stop any ongoing malicious activity.
      • Reset the user’s password and invalidate active sessions.
      • Review and remove any malicious inbox rules or forwarding.
   2. Unblock the user on the Restricted entities page:
      • Go to the Microsoft 365 Defender portal → Email & collaboration → Policies & rules → Threat policies → Restricted entities (or directly to 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 mail again.
   3. Verify the user is now able to send and receive from Outlook and other clients.
   4. Implement preventive measures per Top 10 ways to secure your business data, such as enforcing strong authentication, limiting legacy protocols, and monitoring outbound spam.

If the error persists after unblocking and securing the account, open a support case with Microsoft through the admin center so support can verify and clear any remaining outbound spam blocks.

References:

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