(AzureCXP) fixes MicrosoftDocs/defender-docs-pr#482331

Updated lines 74–78
 Added Related content section with links to:

  1.Troubleshoot email delivery issues with error codes (NDR)
  2.External sender delivery troubleshooting
  3.Common non-delivery report (NDR) codes explained

Author: varuntha-MSFT

defender-office-365/outbound-spam-protection-about.md

@@ -70,3 +70,9 @@ Use the following resources outside of Microsoft 365 to send bulk email:
 - **Use a non-Microsoft bulk email provider**: There are several non-Microsoft bulk email solution providers that you can use to send mass mailings. These companies have a vested interest in working with customers to ensure good email sending practices.
 
   The Messaging, Mobile, Malware Anti-Abuse Working Group (MAAWG) publishes its membership roster at [MAAWG Member Organizations List](https://www.maawg.org/about/roster). Several bulk email providers are on the list, and are known to be responsible internet citizens.
+
+## Related content
+
+* [Troubleshoot email delivery issues with error codes (NDR)](https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/fix-error-code-550-4-4-7-in-exchange-online)
+* [External sender delivery troubleshooting](defender-office-365/external-senders-mail-flow-troubleshooting.md)
+* [Common non-delivery report (NDR) codes explanation](https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/non-delivery-reports-in-exchange-online)