Microsoft 365 Security Audit Guide for 2026: Steps, Checklist & Best Practices

A Microsoft 365 security audit in 2026 is no longer just a Secure Score review. It should validate identity controls in Microsoft Entra ID, email and collaboration protection in Microsoft Defender, endpoint posture in Intune, data governance in Microsoft Purview, audit logging, Copilot readiness, and licensing alignment. Done well, it gives you a prioritized remediation roadmap that reduces risk without disrupting daily work.

What Is a Microsoft 365 Security Audit?

A Microsoft 365 security audit is a structured review of your tenant configuration, identities, devices, data controls, applications, and monitoring capabilities. The goal is to identify misconfigurations, excessive access, unmanaged devices, weak authentication, data exposure, and gaps in threat detection.

In 2026, a complete audit should cover these Microsoft security areas:

• Microsoft Entra ID for identity, access, Conditional Access, MFA, guest access, PIM, and risky sign-ins.
• Microsoft Defender XDR and Microsoft Defender for Office 365 for email, collaboration, endpoint, and incident protection.
• Microsoft Intune for device compliance, configuration, app protection, endpoint privilege, and BYOD controls.
• Microsoft Purview for sensitivity labels, DLP, retention, eDiscovery, audit, insider risk, and Compliance Manager.
• Microsoft Secure Score for security posture tracking and prioritized improvement actions.
• Microsoft 365 admin center for tenant settings, licensing, roles, domains, and service health.

Why Microsoft 365 Security Audits Matter in 2026

Microsoft 365 environments change constantly. New users, guests, Teams, SharePoint sites, OAuth applications, devices, mailbox rules, Copilot adoption, and license changes can all introduce risk. A periodic audit helps you find and fix these issues before they become incidents.

A strong audit helps you:

• Reduce account takeover risk by improving identity and authentication controls.
• Detect excessive admin privileges and stale privileged accounts.
• Harden email against phishing, impersonation, spoofing, malware, and malicious links.
• Reduce SharePoint, OneDrive, and Teams oversharing.
• Prepare data controls for Microsoft 365 Copilot and AI-powered search experiences.
• Improve Microsoft Secure Score with business-appropriate actions.
• Align controls with frameworks such as GDPR, HIPAA, ISO 27001, NIST, and internal governance requirements.
• Confirm that licensing under Microsoft NCE and add-on subscriptions matches your security requirements.

2026 Microsoft 365 Security Audit Framework

Use a framework instead of a one-time checklist. A practical Microsoft 365 audit should review eight domains:

1. Identity and access: Entra ID, MFA, Conditional Access, privileged access, guests, access reviews, and risky sign-ins.
2. Devices and endpoints: Intune compliance, configuration baselines, Defender for Endpoint integration, local admin rights, and unmanaged device access.
3. Email and collaboration: Defender for Office 365, Exchange Online Protection, SharePoint, OneDrive, Teams, external sharing, and mailbox rules.
4. Data protection: Microsoft Purview sensitivity labels, DLP, retention, eDiscovery, audit, and Copilot data exposure readiness.
5. Applications and OAuth: Enterprise apps, app registrations, service principals, consent policies, and SaaS governance.
6. Threat detection and response: Defender XDR incidents, alert tuning, audit logs, Sentinel integration, and response workflows.
7. Compliance and governance: Compliance Manager, records management, lifecycle policies, insider risk, and policy ownership.
8. Licensing and cost alignment: Business Premium, Microsoft 365 E3/E5, Entra ID P1/P2, Defender, Intune, Purview, and NCE subscription fit.

Step 1: Establish Your Security Baseline

Start by documenting the current state of the tenant. Do not change controls blindly until you understand business impact, licensing, and dependencies.

Baseline checks:

• Review Microsoft Secure Score and identify high-impact recommendations.
• Confirm whether Security Defaults are enabled or whether Conditional Access policies are used instead.
• Inventory global admins, privileged roles, emergency access accounts, and delegated partner access.
• Review tenant-wide settings in the Microsoft 365 admin center, Entra admin center, Defender portal, Purview portal, and Intune admin center.
• Export key policy settings for Conditional Access, MFA, Defender for Office 365, sharing, DLP, retention, and device compliance.
• Verify audit logging, alerting, and log retention requirements.

The output should be a baseline report that separates urgent security gaps from optimization items.

Step 2: Audit Identity and Access in Microsoft Entra ID

Identity is the most important control plane in Microsoft 365. If attackers compromise identities, they can reach email, files, Teams, applications, and admin portals.

Review these identity controls:

• Multifactor authentication: Require MFA for all users, with stronger requirements for admins and sensitive roles.
• Phishing-resistant authentication: Evaluate passkeys, FIDO2 security keys, Windows Hello for Business, certificate-based authentication, or authentication strengths where appropriate.
• MFA configuration: Confirm number matching, remove weak or unused methods, and use Temporary Access Pass for secure onboarding and recovery.
• Conditional Access: Enforce risk-based, location-aware, device-aware, and app-aware access policies.
• Legacy authentication: Block legacy protocols that bypass modern MFA protections.
• Privileged Identity Management: Use Microsoft Entra PIM for just-in-time admin activation where licensing supports it.
• Admin roles: Remove standing Global Administrator access when narrower roles are sufficient.
• Break-glass accounts: Maintain emergency access accounts, exclude them carefully from blocking policies, and monitor them aggressively.
• Risky users and sign-ins: Review Entra ID Protection findings and remediation workflows.
• Guest and external users: Review B2B collaboration, guest access, stale guests, cross-tenant access settings, and access reviews.
• Entitlement management: Use access packages and approval workflows for repeatable access governance when available.

Critical identity fixes should normally be the first remediation priority.

Step 3: Audit Email Security and Collaboration Protection

Email remains one of the most common entry points for phishing, malware, business email compromise, and credential theft. Review both Exchange Online Protection and Microsoft Defender for Office 365 settings.

Email and collaboration checks:

• Confirm SPF, DKIM, and DMARC are configured correctly for accepted domains.
• Review Defender for Office 365 preset security policies and determine whether Standard or Strict presets fit the organization.
• Validate anti-phishing, impersonation protection, spoof intelligence, anti-spam, anti-malware, and zero-hour auto purge settings.
• Review Safe Links and Safe Attachments policies where licensed.
• Review quarantine policies and user notification settings.
• Identify risky mailbox forwarding, inbox rules, transport rules, and connectors.
• Review allow/block lists and remove unnecessary permanent allows.
• Review attack simulation training availability and results where Defender for Office 365 Plan 2 or Microsoft 365 E5 capabilities are licensed.
• Review Teams, SharePoint, and OneDrive external collaboration settings together, not in isolation.

Licensing matters here: Defender for Office 365 Plan 1 and Plan 2 provide different capabilities, and Microsoft 365 Business Premium, E3, E5, and add-on plans should be mapped against required protections.

Step 4: Audit SharePoint, OneDrive, Teams, and Copilot Data Exposure

Modern Microsoft 365 security audits must include collaboration and oversharing risk. This is especially important before enabling or expanding Microsoft 365 Copilot, because Copilot respects existing permissions and can surface content users already have access to.

Review these controls:

• External sharing settings for SharePoint and OneDrive.
• Anonymous or anyone links, default link types, link expiration, and download restrictions.
• Site owners, Teams owners, guest members, private channels, and shared channels.
• Sensitivity labels for files, emails, groups, Teams, and SharePoint sites.
• Data Loss Prevention policies for Exchange, SharePoint, OneDrive, Teams, endpoints, and supported apps.
• Overshared sites, stale Teams, orphaned groups, and public access exposure.
• Restricted SharePoint search or site access controls where appropriate for Copilot readiness.
• Microsoft Purview Data Security Posture Management capabilities if available in the tenant.

The goal is not to block collaboration. The goal is to make sharing intentional, governed, and visible.

Step 5: Audit Microsoft Purview Compliance and Data Governance

The former Microsoft 365 Compliance Center capabilities are now positioned under Microsoft Purview. A 2026 audit should use the Microsoft Purview portal to review data protection, compliance, retention, and investigation controls.

Purview checks:

• Compliance Manager improvement actions and assessment templates.
• Sensitivity labels and label publishing policies.
• Data Loss Prevention policies and false-positive handling.
• Retention labels, retention policies, records management, and data lifecycle management.
• eDiscovery configuration and role assignments.
• Purview Audit Standard or Audit Premium availability and retention requirements.
• Communication Compliance policies if applicable.
• Insider Risk Management policies if applicable and legally approved.
• Content search permissions and auditability.
• Regulatory alignment for GDPR, HIPAA, FINRA, ISO, or industry-specific requirements.

Compliance settings should be tied to actual business policies. Avoid enabling sensitive monitoring features without HR, legal, and privacy approval.

Step 6: Audit Devices and Endpoint Security with Intune

A strong Microsoft 365 tenant can still be exposed if users access it from unmanaged, noncompliant, or compromised devices. Microsoft Intune and Microsoft Defender for Endpoint should be reviewed together.

Device and endpoint checks:

• Intune enrollment status for Windows, macOS, iOS, Android, and shared devices.
• Compliance policies for encryption, OS version, jailbreak/root detection, firewall, antivirus, and device health.
• Conditional Access rules that require compliant or hybrid joined devices for sensitive access.
• Intune configuration profiles and security baselines.
• Microsoft Defender for Endpoint onboarding and endpoint detection coverage.
• Attack surface reduction rules, endpoint firewall, antivirus, and tamper protection.
• Local administrator control and Microsoft Intune Endpoint Privilege Management where licensed.
• App protection policies for unmanaged or BYOD devices.
• Windows Autopatch readiness and update rings where appropriate.
• Access restrictions for unmanaged devices downloading files from SharePoint and OneDrive.

This section is especially important for hybrid work, contractors, mobile users, and organizations with BYOD policies.

Step 7: Audit Apps, OAuth Consent, and SaaS Governance

Third-party applications and OAuth permissions are a frequent blind spot. A user-approved app can sometimes access mail, files, calendars, or directory data long after the original business need is gone.

Application governance checks:

• Enterprise applications and app registrations in Microsoft Entra ID.
• Service principals with high privileges or unused credentials.
• OAuth permissions and delegated access grants.
• Admin consent workflow and user consent restrictions.
• Publisher verification and app risk review.
• Expiring client secrets and certificates.
• Unused or stale applications.
• Defender for Cloud Apps discovery, app governance, and session controls where licensed.

Remove unused applications, restrict user consent where appropriate, and document business owners for approved apps.

Step 8: Audit Threat Detection, Logs, Alerts, and Response

Security controls are incomplete without monitoring and response. The audit should confirm that the organization can detect suspicious activity, investigate it, and respond quickly.

Monitoring checks:

• Microsoft Defender XDR incidents, alert policies, and automated investigation settings.
• Microsoft Defender for Office 365 alerts for phishing, malware, and user-reported messages.
• Microsoft Defender for Endpoint alerts and device exposure insights.
• Microsoft Entra sign-in logs, audit logs, risky users, and risky sign-ins.
• Microsoft Purview Audit retention and search requirements.
• Exchange, SharePoint, OneDrive, Teams, and admin activity audit events.
• Alert routing, severity definitions, and response ownership.
• Microsoft Sentinel integration if centralized SIEM/SOAR monitoring is required.
• Executive dashboards for open risks, remediation status, and Secure Score trends.

A good audit should identify not only missing alerts but also noisy alerts that teams ignore.

Step 9: Review Licensing, NCE Commitments, and Security Coverage

Security audits should include licensing because many Microsoft 365 controls depend on specific plans. Under Microsoft New Commerce Experience, subscription term choices, monthly or annual commitments, and add-on decisions affect flexibility and cost.

Review:

• Whether Microsoft 365 Business Premium, E3, E5, or frontline plans match user risk profiles.
• Whether Entra ID P1 or P2 is needed for Conditional Access, Identity Protection, PIM, or access governance scenarios.
• Whether Defender for Office 365 Plan 1 or Plan 2 is required for email security needs.
• Whether Intune is available for device and app protection requirements.
• Whether Microsoft Purview capabilities meet DLP, eDiscovery, audit, and compliance requirements.
• Whether Defender for Endpoint, Defender for Cloud Apps, or Microsoft Sentinel are needed for detection and response goals.
• Unused licenses, overassigned licenses, disabled users with licenses, and security add-ons assigned to the wrong users.

The objective is not to buy every security product. The objective is to align risk, licensing, and operational capability.

Prioritized Remediation Plan

After the audit, convert findings into a remediation roadmap. Prioritize actions based on risk, business impact, licensing, and implementation effort.

Recommended order:

1. Critical identity fixes: MFA, legacy authentication blocking, Conditional Access, admin roles, break-glass monitoring, and risky sign-in response.
2. Email hardening: Defender policies, anti-phishing, DMARC/DKIM/SPF, Safe Links, Safe Attachments, quarantine, forwarding, and transport rule cleanup.
3. Data protection: external sharing, sensitivity labels, DLP, retention, and Copilot readiness.
4. Endpoint compliance: Intune enrollment, compliance policies, Defender for Endpoint, local admin control, and unmanaged device rules.
5. App governance: OAuth consent, enterprise apps, service principals, and risky third-party applications.
6. Monitoring: Defender XDR incidents, Purview Audit, Entra logs, alert routing, and Sentinel integration if needed.
7. Governance cadence: recurring access reviews, Secure Score reviews, policy ownership, and executive reporting.

Each remediation item should include an owner, priority, affected users, licensing dependency, implementation steps, rollback plan, and target completion date.

Common Mistakes to Avoid

• Treating Secure Score as the only audit result instead of one useful input.
• Enabling Conditional Access policies without testing exclusions, emergency access, or user impact.
• Keeping too many permanent Global Administrators.
• Allowing legacy authentication or weak authentication methods to remain active.
• Ignoring guest users, shared channels, and cross-tenant access settings.
• Reviewing email security without checking SPF, DKIM, DMARC, forwarding, and mailbox rules.
• Assuming SharePoint and Teams permissions are safe before enabling Copilot.
• Leaving user consent to third-party apps unrestricted.
• Reviewing compliance features without legal, privacy, and records stakeholders.
• Buying security licenses without operational ownership for the controls they unlock.

Recommended Audit Cadence

For most organizations, a Microsoft 365 security audit should be performed at least annually, with focused reviews more often for high-risk areas.

Suggested cadence:

• Weekly: Review critical Defender incidents, risky users, high-risk sign-ins, and urgent Secure Score changes.
• Monthly: Review admin roles, external sharing, mailbox forwarding, OAuth apps, and device compliance.
• Quarterly: Review Conditional Access, guest access, access reviews, DLP events, Defender policies, and endpoint posture.
• Semiannually: Run phishing simulations, tabletop incident exercises, and Copilot data exposure reviews.
• Annually: Complete a full tenant security audit, licensing review, compliance review, and executive risk report.

Key takeaways

• A 2026 Microsoft 365 security audit should cover Entra ID, Defender XDR, Intune, Purview, Secure Score, apps, data exposure, logging, and licensing.
• Identity controls should be remediated first, especially MFA, phishing-resistant authentication, Conditional Access, legacy authentication, privileged roles, and risky sign-ins.
• Email security requires more than Safe Links and Safe Attachments; review Defender presets, anti-phishing, impersonation protection, SPF, DKIM, DMARC, quarantine, forwarding, and transport rules.
• SharePoint, OneDrive, Teams, and Copilot readiness must be audited together to reduce oversharing and protect sensitive data.
• Licensing under Microsoft NCE should be reviewed alongside security requirements so the tenant has the right capabilities without unnecessary spend.
• The audit should end with a prioritized remediation roadmap, not just a list of findings.

If you want an objective review of your Microsoft 365 security posture, IT Partner can help with a Microsoft 365 Security Assessment that covers Entra ID, Defender, Intune, Purview, Secure Score, Copilot readiness, and licensing alignment, then turns the findings into a practical remediation plan.