Is Microsoft 365 Threat Protection Enough?

Microsoft 365 Defender provides a solid baseline—email filtering, Office app protection and basic endpoint screening—but it’s rarely enough on its own for SMEs; pair it with a third-party EDR or managed detection (MDR) and ongoing 24/7 monitoring to handle targeted threats and regulatory needs, as NCSC recommends.

Many UK firms assume turning on Microsoft 365 threat protection is the final step. After a few months they find targeted phishing and bespoke malware bypass basic rules, or that audit logs and response tools aren’t detailed enough for regulatory or insurance needs.

The takeaway: treat Microsoft 365 as the foundation, not the full stack. That changes your priorities: tighten configuration first, then add detection and response that works with the tenant rather than around it.

Harden the tenant first: configuration, policies and visibility

Start by reducing obvious gaps inside the platform. Enable multi-factor authentication (MFA) for everyone, block legacy authentication, and enforce Conditional Access where you can. Turn on Microsoft Defender for Office 365 features such as Safe Links and Safe Attachments, and ensure Exchange Online Protection (EOP) policies are tuned to your staff profile rather than default settings. Use the Microsoft Secure Score to prioritise quick wins, and export audit logs to a central SIEM or log store so you keep a searchable trail for compliance.

Concrete items to action now:

• Enforce MFA and block legacy auth across all accounts.
• Enable Safe Links/Safe Attachments and set aggressive anti-phishing thresholds for external mail.
• Apply Conditional Access for risky logins and require compliant devices for sensitive apps.
• Configure mailbox audit logging and retain logs for at least 90 days, or longer if your insurer or auditor requires it.

For the security model, follow the NCSC’s layered-defence advice and map each control to a single business risk (data loss, ransomware, impersonation). NCSC’s guidance on layered defences is a useful index when deciding which controls to prioritise.

Add detection, response and continuous monitoring

Once the tenant is tightened, focus on finding and containing what gets through. Microsoft 365 will surface many alerts, but triage and context are the hard parts. Deploy or buy an Endpoint Detection and Response (EDR) product that integrates with Microsoft signals, or use a Managed Detection and Response (MDR) service that ingests Defender telemetry and provides 24/7 analysis. 24/7 monitoring matters because many breaches are discovered outside office hours.

Operational actions that make a measurable difference:

• Integrate Defender alerts into a central incident workflow and set SLA targets for triage (for example, initial review within 1 hour for high priority).
• Choose an EDR/MDR that can quarantine endpoints, roll back malicious files and push forensic data into your SIEM.
• Run tabletop exercises every 6–12 months and rehearse notification and GDPR reporting steps.
• Keep backups isolated from the primary tenant and test restores quarterly.

If you want help tying Defender to active monitoring and response, consider a support partner who can configure alerts, operate integrations and run detection tuning—for example, Microsoft 365 support and managed detection is available from specialist providers who work with your tenant to reduce noise and speed response: Microsoft 365 support and managed detection.

Related reading

• our microsoft 365 support for business guide
• Microsoft 365 security audit service: what UK SMEs need to know
• Microsoft 365 Defender configuration: what to enable and why
• Cost of Microsoft 365 managed services — a practical guide for UK businesses
• Microsoft 365 backup service: a straightforward guide for UK businesses

FAQ

Can Microsoft 365 threat protection stop targeted phishing?

It reduces risk for generic phishing, but targeted (spear‑phishing) often needs additional controls: targeted training, advanced anti-phishing policies, and an EDR/MDR service to catch credential misuse and lateral movement.

Do I need extra logging for GDPR or cyber insurance?

Usually yes—keep mailbox and audit logs for at least 90 days and retain incident records for 6–12 months to satisfy most insurers and meet ICO expectations for incident investigation.

How long does it take to get MDR running with Microsoft 365?

Expect an initial MDR deployment and tuning phase of around 2–6 weeks for a typical 10–200 user organisation, longer if you need complex integrations or custom playbooks.

Will upgrading to Defender for Endpoint remove the need for third‑party EDR?

Defender for Endpoint covers many detection needs but small organisations often still benefit from a third‑party EDR or MDR for proactive threat hunting, 24/7 response and independent forensic capability.