How to Troubleshoot Microsoft 365 Emails Not Reaching External Recipients
Question details
Users need to diagnose and resolve an issue where emails sent from a Microsoft 365 account fail to be delivered to external domains.
- Product
- Microsoft 365 Exchange Online
- Device & OS
- not provided
- Scenario
- Sending outbound emails to external recipients outside the organization's domain.
- Observed behavior
- External recipients do not receive the sent messages, and the sender may or may not receive an automated delivery failure notification.
Check your local Outbox and Sent Items folders to confirm the email was successfully dispatched from your email client before investigating server-level routing issues.
Run a Message Trace in the Exchange Admin Center
Exchange administrators can run a message trace to view the exact delivery status and identify any transport or authentication errors blocking the email.
A message trace follows email messages as they travel through your Exchange Online organization. It is the most definitive way to determine if a message was received, rejected, deferred, or delivered.
Sign in to the Microsoft 365 admin portal with administrator credentials and navigate to the Exchange admin center.
In the left-hand navigation menu, expand 'Mail flow' and select 'Message trace'.
Click 'Start a trace'. Enter the sender's email address in the 'Senders' field and the external recipient's address in the 'Recipients' field. Adjust the time range to cover when the email was sent.
Click 'Search' to run the trace. Review the status column for the specific message. If it says 'Failed' or 'Pending', click on the message row to view detailed error codes and diagnostic information.
Review Non-Delivery Reports (NDRs)
Check your inbox for bounce-back messages which contain specific error codes indicating why the email was not delivered.
Boost Your Productivity with WPS Office
While you are troubleshooting Microsoft 365 email server issues, consider using WPS Office for your document creation and editing needs. It is a highly compatible, free alternative that allows you to easily edit documents and share them via your preferred email client.
- 1. Download and Install: Visit the official WPS Office website to download the free installation package and follow the on-screen instructions.
- 2. Open Your Documents: Launch WPS Office and drag your existing Microsoft Office files into the workspace to open them instantly without formatting loss.
- 3. Edit and Share via Email: Use the built-in 'Share' feature to instantly attach your finished documents to your default email client.
Frequently Asked Questions
Why didn't I receive a non-delivery report (NDR) when my email failed to deliver?
If the recipient's mail server silently drops the email, aggressively filters it as spam, or quarantines it without explicitly rejecting the connection, no NDR is generated back to the sender. A message trace is required to confirm if it successfully left your Microsoft 365 environment.
Can standard users run a message trace in Microsoft 365?
No, standard users do not have the required permissions. You must contact an IT administrator who has access to the Exchange admin center to perform a message trace on your behalf.
What does a 'Pending' status mean in an Exchange message trace?
A 'Pending' status means that the Microsoft 365 server is currently trying to deliver the message but is facing temporary obstacles, such as the recipient server being temporarily offline or applying graylisting. Microsoft 365 will continue to attempt delivery for up to 48 hours.
How long is message trace data kept in Microsoft 365?
By default, basic message trace data is available for up to 10 days. For messages older than 10 days (up to 90 days), administrators must submit a request for an extended historical search, which may take several hours to generate.
