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Fix Outlook Receiving Emails but Replies Bounce Back as Undeliverable
Question details
The user is able to receive incoming messages in Microsoft 365 Outlook, but all outgoing emails, including replies and emails sent to themselves, are bouncing back with an undeliverable error.
- Product
- Microsoft Outlook
- Device & OS
- not provided
- Scenario
- Attempting to reply to incoming emails or send new messages to internal and external recipients.
- Observed behavior
- Outgoing messages fail to send and immediately return a Non-Delivery Report (NDR) bounce-back, despite incoming emails being received without any issues.
Keep the bounced-back email (Non-Delivery Report) in your inbox, as you will need the specific error code it contains to identify the root cause of the delivery failure.
Test Outlook on the Web and Check the NDR Code
This helps determine if the issue is limited to the local Outlook desktop application or if it is a broader account or server issue.
A Non-Delivery Report (NDR) contains diagnostic codes that explain exactly why an email was rejected. Testing via the web version isolates local client issues from server-side problems.
Open the bounced-back email and look for a specific error code (such as 5.1.1, 5.7.1, or similar) to understand why the server rejected the outgoing message.
Open your web browser and sign in to Outlook on the web (OWA) using your Microsoft 365 credentials.
Compose a new message and send it to yourself or a trusted external contact. If the email goes through successfully, your desktop Outlook profile may be corrupt and require repairing.
Verify Exchange Online DNS Records (For Custom Domains)
Use this solution if you are using a custom domain and the webmail test also resulted in an undeliverable bounce-back.
Run a Message Trace to Identify Delivery Failures
Administrators can use this tool to track the exact path of an email and pinpoint where the outbound delivery is failing.
Try WPS Office for a Seamless and Free Productivity Experience
While resolving complex Outlook server or Exchange DNS issues often requires technical troubleshooting and paid Microsoft 365 subscriptions, WPS Office offers a completely free, lightweight, and powerful alternative for all your document processing needs.
- 1. Visit the WPS Website: Go to the official WPS Office website on your computer.
- 2. Download the Installer: Click the 'Free Download' button to get the correct version for your operating system.
- 3. Install and Launch: Run the setup file and open WPS Office to immediately start creating or editing your documents.
Frequently Asked Questions
Why do my emails bounce back when sending to my own email address?
This can happen if your domain's DNS records, particularly MX or SPF, are misconfigured. It can also occur if your mailbox has reached its storage quota or if there is a corrupted auto-complete entry in your Outlook cache.
What is an NDR and where do I find the error code?
A Non-Delivery Report (NDR) is the automated email you receive when a message fails to send. The error code (typically formatted as 5.x.x) is located inside the body of the bounce-back email, along with a brief explanation of why the delivery failed.
Can repairing my Outlook profile fix an undeliverable message error?
Yes, if the error is caused by local corruption or a malfunctioning Outbox. You should first test by sending an email via Outlook on the web. If the webmail sends successfully, repairing or recreating your local Outlook profile is the recommended fix.
How do I check if my Microsoft 365 mailbox is restricted?
If an account sends too many spam-like emails, Microsoft may restrict it from sending outbound mail. A Microsoft 365 administrator can check this by logging into the Microsoft 365 Defender portal and reviewing the 'Restricted users' page.
