What Is a Microsoft 365 Security Audit? A Complete Guide for US Businesses

If your company runs on Microsoft 365, then Microsoft 365 holds a large part of your business. Email, contracts, spreadsheets, customer records, payroll files and internal chat all live in one connected system. That convenience is the reason attackers like it too. One compromised account can open a door to many places.

A Microsoft 365 security audit is the way you find out how well that system is protected. It is a structured review of your tenant's settings, access and records, carried out against a clear scope and a set of reference standards, and it ends with a report that tells you what is working, what is not and what to fix first.

This guide explains what a Microsoft 365 security audit is in plain terms. It covers who needs one, what it looks at, how the process runs from first call to final report, what typical findings look like, how it differs from related activities, and what to do after you receive the results. It is written for US business owners, IT managers and anyone who has been asked, "Have we had a security audit of our Microsoft 365 setup?" and does not yet have a good answer.

What a Microsoft 365 security audit actually is

Start with the word "tenant." Your organisation's Microsoft 365 environment is called a tenant. It is the container that holds your users, groups, licences, mailboxes, sites, apps and policies. A security audit examines that tenant to answer a simple question: do the controls we intended to have match the access the tenant really allows?

That distinction matters. Many organisations believe they have MFA, restricted sharing and strong email protection because someone configured those things at some point. An audit checks the present reality: which users are covered, which are excluded, what the policies do in practice and what evidence supports the conclusion.

An audit is not magic. It does not predict the future or promise you will never be attacked. It gives you an evidence-based picture of your current position, ranked by risk, with practical steps to improve it. For a professional example of how a scoped, evidence-led engagement is described, see this Microsoft 365 security audit service from Atlant Security.

Who needs one

Almost any organisation using Microsoft 365 can benefit, but some situations make an audit more urgent:

• You have never had one. If the original setup was done years ago and nobody has reviewed it since, there is likely drift.
• Cyber insurance is up for renewal. Insurers ask detailed questions, and you want accurate answers backed by evidence.
• You handle regulated data. Healthcare providers (HIPAA), financial firms (FTC Safeguards Rule, GLBA), defence contractors (CMMC and NIST SP 800-171) and companies seeking SOC 2 all have reasons to document their controls.
• A customer or partner asks for proof. Larger customers increasingly include security questionnaires in contracts.
• You have had an incident or a near miss. An audit helps find root causes and similar weaknesses.
• You are planning a change. Mergers, tenant migrations and Microsoft 365 Copilot rollouts all benefit from a clean-up first.
• Your IT team is stretched. A review gives a short, prioritised list of what matters most.

Small businesses are not exempt. A 15-person firm with a single compromised mailbox can lose real money. The audit can simply be smaller.

What a Microsoft 365 security audit covers

The exact scope depends on your needs and licences. Most audits are built around the following areas.

Identity and access

Identity is the front door. An audit looks at multi-factor authentication coverage, Conditional Access policies and their exclusions, legacy authentication, privileged role assignments, emergency access accounts, guest users, service accounts and password and authentication method settings. The core question is who can sign in, how they prove who they are and what happens when something looks unusual.

Email and messaging security

Email remains the most common entry point for attacks. The audit reviews SPF, DKIM and DMARC records, anti-phishing and anti-malware policies, Safe Links and Safe Attachments if you have Defender for Office 365, transport rules, connectors, mailbox forwarding, mailbox permissions and user reporting of phishing.

Collaboration and data sharing

This covers SharePoint, OneDrive and Teams. The audit looks at tenant sharing settings, site-level overrides, anonymous links, guest access, team and site ownership, and where sensitive data lives. It also considers Microsoft Purview features such as sensitivity labels and data loss prevention.

Devices

If you use Intune, the audit reviews compliance policies, app protection policies and how device state feeds into access decisions. Even without Intune, it may note how unmanaged devices reach company data.

Applications and integrations

Enterprise applications, app registrations, OAuth consent grants and user consent settings are checked for over-permissioned or unknown apps. This is a growing source of risk because these access paths sit outside a simple user-and-MFA checklist.

Logging, monitoring and response readiness

An audit confirms that the Purview audit log is on, how long records are kept, whether mailbox auditing is enabled, what alerts exist and who sees them. The aim is to find out whether you could investigate an incident if you had to.

Governance and ownership

Finally, a good audit asks who owns each area. Settings without owners drift. The review may look at change processes, documentation and review routines.

The audit process, step by step

Although details vary, most Microsoft 365 security audits follow a similar path.

Step 1: Define goals and scope. The provider or internal lead agrees with you why the audit is happening, which tenants and workloads are included, what evidence period applies, who will see the report and any constraints such as NDAs or restricted systems.

Step 2: Confirm licences. Licences determine which controls are available. A good audit begins with an inventory by user group, so recommendations fit what you own.

Step 3: Arrange access and evidence gathering. The safest methods are supervised screen sessions with your administrators, read-only roles such as Global Reader and Security Reader, or approved exports. Credentials should never be shared through a web form or email.

Step 4: Review the tenant. The auditor works through identity, email, collaboration, devices, apps and logging. They use a mixture of portals, PowerShell, Microsoft Graph and baseline tools, and they capture evidence along the way.

Step 5: Validate findings with your team. Before the report is final, the auditor discusses draft findings with your administrators. This corrects factual mistakes and surfaces business reasons for certain settings.

Step 6: Deliver the report. The report includes an executive summary, a prioritised list of findings, supporting evidence, recommended actions, effort estimates and licence dependencies.

Step 7: Plan remediation. You agree owners, dates and order of work. Remediation may be done by your team, by the auditor under a separate agreement or by another partner.

Step 8: Revalidate. After fixes, someone checks that they work and that they did not break anything. Closing the loop is what turns a report into an improvement.

What typical findings look like

Every tenant is different, but certain patterns show up often. These are examples of the kind of finding an audit produces:

• MFA coverage gaps: A Conditional Access policy requires MFA, but an exclusion group contains accounts that nobody can explain.
• Legacy authentication still allowed: Some older apps or protocols can sign in without modern MFA.
• Too many privileged accounts: Several Global Administrators, including some who also use the same account for daily email.
• External sharing is more open than intended: Anonymous links with no expiry and sites that override tenant settings.
• Unreviewed guest accounts: External users from completed projects who still have access.
• Risky app permissions: Third-party apps with broad access to mail and files.
• Weak email authentication: DMARC set to monitoring only, or DKIM not enabled on custom domains.
• Limited logging: Audit retention shorter than you would need for an investigation.
• No clear ownership: Security settings with no named owner and no review cycle.

Each finding in a good report explains what was observed, where the evidence is, why it matters, what to do and how to confirm the fix. It also distinguishes between "we saw this," "we looked and did not see it" and "we could not verify this." That honesty is what separates an audit from a sales exercise.

How an audit differs from related activities

People often mix up several different security activities. A short comparison helps.

Secure Score review. Microsoft Secure Score lists recommended actions and gives a percentage. It is a useful input. An audit goes further by checking coverage, exceptions, licence fit and evidence. Secure Score does not express the probability of a breach.

Security assessment. In everyday use, "audit" and "assessment" overlap. Strictly speaking, an audit measures against a defined standard with documented evidence, while an assessment is often broader and more advisory. Always check what a provider means and focus on the deliverable.

Penetration test. A penetration test actively tries to break in by simulating an attacker. An audit reviews configuration and evidence without attacking. They answer different questions and work well together.

Compliance audit. A compliance audit, such as for SOC 2 or HIPAA, checks against a formal framework and is typically performed by qualified auditors. A Microsoft 365 security audit can support compliance by producing evidence, but it does not replace a formal attestation.

Managed security monitoring. This is ongoing watching and response. An audit is a point-in-time review that improves what monitoring has to watch.

US regulatory and insurance drivers

You do not need a regulator to justify an audit, but US rules and market pressure make evidence more valuable.

HIPAA. Covered entities and their business associates must protect electronic protected health information. The Security Rule expects risk analysis and access controls. A Microsoft 365 audit can support those by documenting how email, files and identities are protected.

FTC Safeguards Rule. Applies to many non-bank financial institutions, such as tax preparers, mortgage brokers and some auto dealers. It requires a written information security programme, including access controls, MFA and encryption.

CMMC and NIST SP 800-171. Defence contractors that handle controlled unclassified information must meet specific controls. Microsoft 365 configuration is a big part of that, especially identity, logging and data handling.

SOC 2. Service providers use SOC 2 to show customers they have effective controls. Auditors will ask for evidence of access reviews, logging and change management.

State laws. Many US states have breach notification laws and some have specific data security requirements. The details vary, so check with legal counsel.

Cyber insurance. Insurers commonly ask whether MFA is enforced for all users, whether email is filtered, whether backups are tested and whether logging exists. Accurate answers matter, because incorrect statements can affect claims.

None of this is legal advice. If a framework applies to you, work with a qualified compliance adviser and use the audit as one source of evidence.

What to do after the audit

Getting the report is the beginning. To benefit from it:

1. Read the executive summary first. Make sure leadership understands the top risks and what is needed.
2. Sort findings into three groups. Quick fixes with what you already own, changes that need budget or a licence upgrade, and process or people issues.
3. Assign owners and dates. Every finding needs a name and a target.
4. Pilot risky changes. Use report-only modes and small test groups for changes that may affect users.
5. Document exceptions. Where you accept a risk, write down who accepted it and when it will be reviewed.
6. Revalidate. Confirm that fixes work, ideally 60 to 90 days later.
7. Schedule the next review. Put the following audit and quarterly check-ins in the calendar now.

Keep the report safe. It describes your weaknesses, so limit who can read it and store it in a restricted location.

How to choose between doing it yourself and hiring help

You can run a basic review internally using the admin centres, Secure Score and PowerShell. This works well for routine checks and for organisations with skilled administrators who have time. An independent audit is worth considering when you want objectivity, when the tenant is large or complex, when insurers or customers want independent evidence, or when your team does not have the capacity.

If you hire help, ask how they gain access, what evidence they provide, how they treat your licences, what the report looks like and whether remediation is separate. Insist on a written scope and price before work begins.

Frequently asked questions

How long does a Microsoft 365 security audit take?

Small, focused reviews can be completed in a matter of days. Larger or hybrid tenants take longer. Timelines depend on scope, access and how quickly evidence is provided.

How much does it cost?

Cost depends on the number of tenants, users, workloads and compliance needs. Ask for a written quote based on a defined scope. A separate article in this series covers cost in more detail.

Will the audit disrupt our staff?

Normally not. A standard review reads settings and logs and does not change anything. Any active testing, such as phishing simulations, should be agreed separately.

Do we need to give the auditor administrator passwords?

No. Use supervised sessions or read-only access, and never share credentials casually.

What if we use another security product alongside Microsoft 365?

Include it in the scope if it affects the tenant. Third-party mail filters, identity providers and endpoint tools can change the effective protection.

Is an audit a one-time activity?

It should not be. Tenants change constantly. Plan an annual audit with lighter quarterly checks and extra reviews after major changes.

Final thoughts

A Microsoft 365 security audit is a practical tool. It tells you whether the protections you think you have are real, shows you where the largest risks sit and gives you a plan to reduce them. It also gives you evidence to share with insurers, customers and regulators, which is increasingly valuable in the US market.

You do not need to start big. Choose the areas that matter most, usually identity and email, confirm your licences, write down the scope and make sure someone owns the follow-up. If you would like independent help, Atlant Security offers evidence-led reviews with licence-aware recommendations and clear reporting. Whatever route you pick, the best time to find out how your tenant really behaves is before someone else does.