1. Verify System Date and Time
- In Windows, go to Settings → Time & Language → Date & Time.
- Enable both "Set time automatically" and "Set time zone automatically" to avoid future mismatches.
2. Install All Available Windows Updates
- Open Settings → Windows Update.
- Make sure your system receives security patches and updated root certificates essential for certificate validation.
3. Test SSL Certificate Using a Browser
- Open your browser and visit the email server’s webmail URL.
- Look for certificate warnings like “Connection not secure” or “Certificate not valid.”
- If you see errors, the problem lies with the server's SSL certificate.
4. Turn Off SSL/HTTPS Scanning in Antivirus
- Temporarily disable any “HTTPS scanning” or “SSL inspection” features in your antivirus or firewall software.
- Test Outlook again—if it connects properly, the scanning tool is likely causing the issue.
5. Use a Clean Network
- Switch to another network (like a mobile hotspot) to rule out network-level SSL interference from corporate firewalls or proxies.
6. Reset Windows SSL Cache
- Press Windows + R, type inetcpl.cpl, go to the Content tab, and click Clear SSL state.
- Restart your PC and test Outlook again.