Websocket connections to critical Microsoft 365 domains

Worth to take a loo at this:

1. Check Firewall & Proxy Rules
• Ensure WebSocket traffic is explicitly allowed for Microsoft 365 domains (*.cloud.microsoft, *.static.microsoft, etc.).
• Some proxies may still block WebSocket connections even if HTTPS inspection is bypassed.
2. Verify Microsoft 365 Network Insights
• Go to Microsoft 365 Admin Center → Network Connectivity Insights.
• Look for any service health notifications related to WebSocket failures.
3. Test WebSocket Connectivity
• Use tools like wss://echo.websocket.org to verify WebSocket connections.
• If external WebSocket connections work but Microsoft 365 fails, the issue is likely tenant-specific.
4. Check TLS Decryption Settings
• Some security appliances perform TLS decryption, which can interfere with WebSocket traffic.
• Ensure Microsoft 365 domains are excluded from TLS decryption.