Configure Microsoft 365 Partner Connector

A Microsoft 365 Partner Connector helps Exchange Online recognize trusted NINJIO sending infrastructure and can reduce delivery delays or failures caused by Microsoft IP throttling.

How-to instructions

1. Sign in to the Exchange admin center and navigate to Mail flow → Connectors → Add a connector.
2. Under New connector, select:
   • Connection from: Partner organization
   • Connection to: Office 365
3. Click Next.
4. Under Connector name, enter NINJIO Phishing Simulation.
5. Ensure Turn it on is selected, then click Next.
6. Under Authenticating sent email, select:
   By verifying that the IP address of the sending server matches one of the following IP addresses, which belong to your partner organization.
7. Add all NINJIO SMTP sending IP addresses listed in our Domains and IPs for Allowlisting article. Click Next.
8. Under Security restrictions, select: Reject email messages if they aren't sent over TLS.
   Leave certificate subject-name restrictions unselected unless specifically instructed by NINJIO. Click Next.
9. Under Review connector, verify the configuration and click Create connector.
10. Confirm that the new connector is Enabled under Mail flow → Connectors.
11. Send a NINJIO test phishing simulation to verify successful delivery.

Notes

• Microsoft throttling: This configuration follows Microsoft's documented approach to mitigating IP throttling, including errors such as 451 4.7.500 Server busy. It does not guarantee that all Microsoft delivery restrictions will be eliminated.
• Microsoft Defender: This connector does not replace Microsoft 365 phishing simulation allowlisting. Ensure Microsoft Defender Advanced Delivery is also configured.
• Third-party security: If your organization uses Proofpoint, Mimecast, or another email security gateway, additional configuration may be required.

Microsoft Reference

Fix NDR error code 451 4.7.500–699 (ASxxx) in Exchange Online