Microsoft 365 (M365) is a powerful platform for collaboration and productivity—but with great power comes great responsibility. Out of the box, M365 offers a strong foundation, but without a few key security tweaks, your organization could be exposed to unnecessary risks.
Whether you’re managing a small business or a large enterprise, here are some basic but essential security measures you should have in place to better protect your Microsoft 365 environment.
🔐 1. Enforce Multi-Factor Authentication (MFA)
MFA is your #1 defense against account compromise. A stolen password alone shouldn’t give an attacker full access to your environment.
• Enforce MFA for all users, especially administrators.
• Use conditional access policies to make MFA smoother (e.g., not required on trusted devices or networks).
• Prefer app-based or hardware-based MFA over SMS.
👑 2. Reduce the Number of Global Admins
Too many Global Admins = too much risk.
• Follow the principle of least privilege—assign the minimum role necessary for each user.
• Use Privileged Identity Management (PIM) to give time-limited admin access when needed.
• Monitor and audit privileged role assignments regularly.
🧠 3. Enable Security Defaults (or Use Conditional Access)
Microsoft offers Security Defaults as a simple baseline for organizations without custom policies:
• MFA for all users
• Blocking legacy authentication
• Protecting privileged accounts
If you need more control, Conditional Access is the next step up—offering granular control over when and how users access services.
📨 4. Monitor and Restrict Email Forwarding
Auto-forwarding rules can be abused to silently exfiltrate emails.
• Disable external auto-forwarding where not needed.
• Use Exchange mail flow rules or Defender for Office 365 policies to alert on suspicious behavior.
• Review forwarding rules as part of regular audits.
👁️ 5. Turn on Audit Logging
Audit logs are critical for incident response and forensic investigations.
• Ensure unified audit logging is turned on in the Microsoft Purview compliance portal.
• Regularly review audit logs or use a SIEM solution to detect anomalies.
• Store logs securely and for as long as needed to meet compliance requirements.
🧪 6. Test with a Honeypot (Optional but Cool)
If you want to get a bit more advanced, consider using a Canarytoken or decoy account to detect unauthorized access.
• Create a fake admin account and monitor logins.
• Deploy a decoy document with a token that alerts when opened.
• Monitor these alerts with automation (e.g., Power Automate, Sentinel).
🧰 7. Use Microsoft Secure Score
Microsoft provides a built-in Secure Score that gives you tailored recommendations for improving your M365 security posture.
• Access it via the Microsoft 365 Defender portal.
• Track improvements over time.
• Prioritize actions with the biggest impact.
Final Thoughts
You don’t need a full security team to make a meaningful difference in your Microsoft 365 setup. By enabling just a few of these basic protections, you can dramatically reduce your attack surface and improve your organization’s resilience to common threats.
Start small. Review regularly. Stay secure.