'%3e%3cpath%20d='M8%200C12.4183%200%2016%203.58172%2016%208C16%2012.4183%2012.4183%2016%208%2016C3.58172%2016%200%2012.4183%200%208C0%203.58172%203.58172%200%208%200ZM11.6162%204.38379C11.2257%203.99337%2010.5927%203.99338%2010.2021%204.38379L8%206.58594L5.79785%204.38379C5.40732%203.99334%204.77429%203.99329%204.38379%204.38379C3.99331%204.77429%203.99335%205.40733%204.38379%205.79785L6.58594%208L4.38379%2010.2021C3.99348%2010.5927%203.99341%2011.2257%204.38379%2011.6162C4.77426%2012.0066%205.40734%2012.0065%205.79785%2011.6162L8%209.41406L10.2021%2011.6162C10.5927%2012.0066%2011.2257%2012.0067%2011.6162%2011.6162C12.0067%2011.2257%2012.0066%2010.5927%2011.6162%2010.2021L9.41406%208L11.6162%205.79785C12.0066%205.40735%2012.0066%204.77429%2011.6162%204.38379Z'%20fill='%23080E17'%20fill-opacity='0.46'/%3e%3c/g%3e%3cdefs%3e%3cclipPath%20id='clip0_3761_713'%3e%3crect%20width='16'%20height='16'%20fill='white'/%3e%3c/clipPath%3e%3c/defs%3e%3c/svg%3e)
Fix Microsoft 365 Emails Rejected as Spam to External Recipients
Question details
Users need to resolve an issue where emails sent from Microsoft 365 to external recipients bounce back with a non-delivery report (NDR) stating they were blocked as spam.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Sending email messages to external recipients outside the organization.
- Observed behavior
- All outbound messages sent to external contacts receive a bounce-back non-delivery report (NDR) indicating that the receiving server blocked or rejected the email as spam.
Before proceeding with technical fixes, check if the issue occurs in both the Outlook desktop app and Outlook on the web, and verify if other users in your organization are experiencing the exact same delivery failures.
Review Account Restrictions and Anti-Spam Policies (For Admins)
IT administrators should check the Microsoft 365 Admin Center for outbound spam restrictions or misconfigured mail-flow rules causing the rejections.
When bulk emails are sent or an account exhibits suspicious behavior, Microsoft 365 may temporarily restrict outbound mail. An admin needs to clear these restrictions and verify active policies.
Navigate to the Microsoft 365 Defender portal and sign in with global administrator credentials.
Go to 'Review' > 'Restricted entities'. If the affected user account is listed, select it and choose 'Unblock' to restore sending privileges.
Navigate to 'Email & collaboration' > 'Policies & rules' > 'Threat policies' > 'Anti-spam'. Ensure the outbound anti-spam policy is not overly restrictive or blocking the user.
Open the Exchange Admin Center, go to 'Mail flow' > 'Message trace', and trace the blocked messages to identify the exact transport rule or policy causing the rejection.
Verify Domain Authentication Records (SPF, DKIM, DMARC)
Ensure your custom domain is properly authenticated via DNS records so external email servers trust your messages rather than flagging them as spam.
Open a Support Request with Microsoft
If internal checks and DNS verifications do not resolve the issue, contact Microsoft 365 Support to investigate deeper server-side routing issues.
Looking for a Lightweight Alternative to Microsoft Office?
While resolving complex email server and spam routing issues requires Microsoft admin access, everyday document creation shouldn't be a hassle. Try WPS Office, a powerful and free alternative for Word, Excel, and PowerPoint that keeps you productive.
- 1. Download WPS Office: Visit the official WPS website and download the installer tailored for your operating system.
- 2. Install the Software: Run the setup file and follow the quick on-screen instructions to complete the installation.
- 3. Edit Your Documents: Launch WPS Office to seamlessly open, edit, and save your existing Microsoft Office files without formatting loss.
Frequently Asked Questions
Why am I suddenly getting non-delivery reports (NDRs) stating my emails are spam?
Your Microsoft 365 account might be temporarily restricted due to suspicious outbound activity, or the receiving server's anti-spam policies have become stricter. Misconfigured domain settings can also trigger sudden rejections.
What are SPF and DKIM records?
SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) are essential DNS records that authenticate your custom domain. They prove to external email servers that your messages are legitimate and help protect your domain from spoofing.
Can I fix this email bounce issue without administrator access?
If you are using a corporate or organizational Microsoft 365 account, you generally cannot fix this yourself. Most outbound spam restrictions and mail-flow rule adjustments require an IT administrator to log into the Microsoft 365 Admin Center.
