Zero Trust for Microsoft 365, Explained Without the Buzzwords

"Zero Trust" has been marketed into meaninglessness. Vendors will happily sell you a Zero Trust box. But inside Microsoft 365, Zero Trust is just three honest questions asked on every request:

1. Is this identity who it claims to be?
2. Is this device healthy and known?
3. Should this identity, on this device, reach this data right now?

Verify explicitly

Every access decision uses real signals — user risk, sign-in risk, device compliance, location. In Microsoft 365 that means Entra ID Conditional Access as your policy engine, fed by Identity Protection and Intune device compliance.

Use least-privilege access

Standing global admin is the enterprise equivalent of leaving your keys in the ignition. Use Privileged Identity Management (PIM) so admin roles are:

• Just-in-time (activated when needed, expired automatically)
• Approval-gated for the sensitive roles
• Fully audited

Assume breach

Design as if an attacker already has a foothold. That changes your priorities:

• Segment access so one compromised identity doesn't reach everything.
• Turn on Microsoft Purview DLP and sensitivity labels so data defends itself.
• Instrument Defender XDR and Sentinel so you see the intrusion early.

The Microsoft 365 Zero Trust starter map

| Pillar | Primary tool | First move | | --- | --- | --- | | Identity | Entra ID + Conditional Access | Require MFA, block legacy auth | | Endpoints | Intune | Compliance policies + ASR | | Data | Purview | Sensitivity labels + DLP | | Visibility | Defender XDR / Sentinel | Onboard logs, baseline detections |

Zero Trust isn't a finish line — it's a posture. Start with identity (that's where 90% of breaches begin), then work outward to devices and data. Every step you take shrinks the blast radius of the next incident.