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How to Fix Email Messages Blocked by Outlook or Exchange
Question details
The user needs to diagnose and resolve an issue where an email message is being blocked and returned with a server error by Outlook or Exchange.
- Product
- Microsoft Outlook / Exchange
- Device & OS
- not provided
- Scenario
- Sending an email message that fails to reach the recipient due to a server-side block.
- Observed behavior
- The email is blocked and the user receives an error containing a server name (e.g., DB1PEPF000509E2.eurprd03.prod.outlook.com), which does not provide enough information on its own to identify the root cause.
Ensure you have access to the original bounce-back email notification, specifically the non-delivery report (NDR), as it contains the vital diagnostic codes required for troubleshooting.
Collect and Analyze the Non-Delivery Report (NDR)
Gather the complete non-delivery report and verify your account type to diagnose the exact reason why the email was blocked.
Server names alone cannot pinpoint why an email was blocked. You must retrieve the full non-delivery report (NDR), which contains specific diagnostic codes and routing information necessary for IT administrators or support teams to resolve the issue.
Locate and open the email notification in your inbox that indicates your message was blocked, rejected, or undelivered.
Scroll through the non-delivery report (NDR) to find the specific diagnostic error codes, sender and recipient information, and the complete error text.
Determine whether your mailbox is a Microsoft 365 business or education account, a personal Microsoft account (like Outlook.com or Hotmail), or a standard POP/IMAP account.
Share the full NDR details and your email account type privately with your IT administrator or Microsoft Support team to have the server block investigated and lifted.
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Frequently Asked Questions
What is a Non-Delivery Report (NDR) in Outlook?
An NDR is an automated message generated by the email server informing the sender that an email could not be delivered. It contains diagnostic codes and server details that help identify the exact cause of the delivery failure.
Why does the NDR error only show a server name?
Sometimes the initial error preview only displays the server name (like eurprd03.prod.outlook.com) where the block occurred. To find the exact reason, you need to open the full NDR message and locate the specific diagnostic error code contained within the email body.
How do I share my NDR securely with my IT administrator?
Take screenshots or carefully copy the text of the complete NDR and send it directly to your IT administrator via a secure internal messaging tool or a direct IT support ticket, ensuring sensitive sender and recipient information is kept private.
