Microsoft 365 Security Best Practices

Microsoft 365 security best practices are the configuration and governance steps that harden a Microsoft 365 tenant against account takeover, phishing, ransomware, and data loss. Out of the box, Microsoft 365 is functional but not fully secured — the controls below close the gaps that attackers exploit most often.

A useful way to measure progress is Microsoft Secure Score, a built-in rating of your tenant's security posture. In a recent hardening engagement for a Dubai business, Isstah raised a client's Microsoft Secure Score from 72.4% to 74.3% and its Identity Secure Score from 53% to 54.8% by methodically applying the practices below.

1. Secure identity first

• Enforce multi-factor authentication for every user, ideally via Conditional Access policies rather than per-user settings.
• Block legacy authentication protocols, which bypass MFA and are a favourite of attackers.
• Protect admin accounts: use separate, dedicated admin identities and limit the number of Global Admins.
• Enable self-service password reset (SSPR) and risk-based sign-in policies where licensing allows.

2. Harden email (Exchange Online)

• Configure anti-phishing, anti-spam, and anti-malware policies in Microsoft Defender for Office 365.
• Set up SPF, DKIM, and DMARC to stop domain spoofing.
• Disable automatic external mail forwarding to prevent silent data exfiltration.

3. Protect data (Purview & SharePoint/OneDrive)

• Apply sensitivity labels and basic data loss prevention (DLP) policies to protect confidential information.
• Control external sharing on SharePoint and OneDrive — default to the least-permissive setting that the business needs.
• Enable audit logging and retention so you can investigate incidents later.

4. Defend endpoints (Defender & Intune)

• Onboard devices to Microsoft Defender for Endpoint for EDR-grade protection.
• Use Microsoft Intune to enforce device compliance, encryption, and app policies before granting access.

5. Monitor and review

Hardening Microsoft 365 is a process, not a one-time switch. Isstah's cloud integration services deliver M365 deployment and security hardening for businesses across the GCC, and our case studies show the measurable Secure Score gains we've achieved. Request a Microsoft 365 security review.

Frequently asked questions

What is Microsoft Secure Score?

Microsoft Secure Score is a built-in measurement of an organisation's security posture across its Microsoft 365 tenant. A higher score reflects more recommended security controls in place. It's a practical way to benchmark and track hardening progress over time.

Is Microsoft 365 secure by default?

Microsoft 365 includes strong security capabilities, but the default configuration is not fully hardened. Important protections such as enforced MFA, blocking legacy authentication, anti-phishing policies, and restricted external sharing typically need to be configured and maintained.

What is the single most important Microsoft 365 security setting?

Enforcing multi-factor authentication for all users — ideally through Conditional Access — while blocking legacy authentication protocols. Together these stop the large majority of account-takeover attacks against Microsoft 365 tenants.

Can Isstah harden our Microsoft 365 environment?

Yes. Isstah provides Microsoft 365 deployment and security hardening for businesses across the GCC, covering identity, email, data protection, and endpoint controls, with measurable Secure Score improvement and full handover documentation.

About the author — Written by the Isstah Technologies team. Isstah Technologies is a Dubai-based IT and cybersecurity system integrator serving businesses across the GCC, delivering cybersecurity, cloud integration, network & infrastructure, and digital transformation. Need help putting this into practice? Talk to our Dubai team for a free consultation.