Microsoft 365 Security Audit Checklist: 15 Tests and Evidence to Collect

A Microsoft 365 security audit is a structured review of identity, email, collaboration, devices, monitoring and recovery. For small businesses in Massachusetts and Rhode Island, the purpose is to identify gaps that can lead to account compromise, sensitive-data exposure and disruption.

A good audit asks what protection is required, what is actually configured, who and what it covers, and whether the business can produce evidence that it works. Microsoft Secure Score helps prioritize recommendations but is not a certificate of security or regulatory compliance.

Record verified domains, subscription types, active users, privileged accounts, devices, business-critical apps and external administrators. Capabilities differ by license: for example, Microsoft Entra Conditional Access licensing and premium risk features are not identical across subscriptions.

Use authorized administrative access, keep evidence in a secure repository and avoid exporting passwords, secrets or unnecessary personal records.

Work through these checks and capture the effective policy, population covered, date, exception and remediation owner. A configuration screenshot alone is not proof that a policy is enforced.

MFA registration is not the same as effective enforcement. Review Microsoft Entra policies and sign-in logs to confirm intended coverage. Prioritize phishing-resistant methods for high-risk privileged access where feasible.

Inspect legacy authentication paths and application dependencies before blocking them. Apply least privilege to administrative roles and test emergency access. If deploying Conditional Access, validate policy effects in report-only mode and protect recovery accounts from accidental lockout.

For additional context, read https://metaitpro.com/conditional-access-explained and the existing introductory checklist at https://metaitpro.com/microsoft-365-security-checklist.

Review anti-phishing, anti-spam, anti-malware and applicable Safe Links or Safe Attachments policies. Verify the actual users and domains assigned to each policy. Review automatic external forwarding and mailbox rules for unauthorized data movement.

Check SPF, DKIM and DMARC together, including third-party systems such as CRM, accounting software and email gateways. A restrictive DMARC policy should follow a verified sender inventory and review of authentication reports.

Inventory enterprise applications and OAuth permissions that can access email or files. Remove unused integrations through an approved process and review the need for broad consent grants.

Review SharePoint and OneDrive external sharing at both tenant and site levels. Examine sensitive sites and anonymous links. Review Teams membership, guest accounts and ownership of inactive workspaces.

Compare the device inventory with Intune or other management tools and the endpoint security console. Investigate unsupported systems, missing EDR agents and encryption exceptions.

Microsoft Purview audit availability and retention depend on subscription and configuration. Verify that relevant events are generated and searchable; do not assume auditing is enabled or retained for a specific period without checking current Microsoft guidance.

Distinguish recycle-bin and retention features from independent backup and recovery. Test a representative restoration and record results, recovery time and limitations. See https://metaitpro.com/does-microsoft-365-need-backup.

Classify issues by likelihood, impact, exposure and business criticality. An unprotected administrator or suspicious forwarding rule may require immediate investigation; a missing policy owner may be scheduled as a governance improvement.

For each finding, capture affected system, evidence, risk, responsible owner, remediation date, verification result and any approved exception. A Microsoft Secure Score improvement action should not be marked complete solely because it was assigned.

Week 1: establish tenant ownership, licensing, MFA, privileged roles and legacy authentication; address urgent exposures immediately.

Week 2: review email security, forwarding, domain authentication, app consent and external sharing.

Week 3: validate device coverage, audit logs, monitoring and backup restoration.

Week 4: verify changes, document remaining exceptions, assign owners and schedule the next review. This timeline is an example, not a Microsoft requirement.

How often should a small business audit Microsoft 365? A comprehensive annual review is a reasonable baseline, supplemented by ongoing monitoring and additional reviews after major changes; regulated organizations may require more frequent checks.

Is Secure Score sufficient? No. It identifies recommendations but does not prove complete coverage, recovery capability or regulatory compliance.

Does Business Premium secure everything automatically? No. Included tools still need configuration, deployment, monitoring and operational ownership.

Can the audit be performed without downtime? Many read-only checks can, but policy changes and recovery tests require planning and approval.

What should the business receive? A tenant inventory, evidence-based findings, risk priorities, remediation owners and follow-up verification.

Meta IT Pro helps small businesses, CPA firms, healthcare practices, nonprofits and law offices in Massachusetts and Rhode Island verify Microsoft 365 identity, email, endpoint and recovery safeguards.

Explore https://metaitpro.com/microsoft-365-services and https://metaitpro.com/managed-email-security, or request a scoped security assessment at https://metaitpro.com/contact. A technical audit does not by itself certify HIPAA, 201 CMR 17.00 or insurance compliance.