Microsoft 365 Security Review: A Practical Guide for UK SMEs.

1. Identity comes first

Why Microsoft 365 security starts with the sign-in.

Microsoft 365 contains valuable information and administrative control, so identity is the natural starting point. If an attacker takes over a user's mailbox, they may gain access to sensitive conversations, documents and password-reset messages. If they compromise a privileged account, the impact can be much larger.

For smaller organisations, the practical question is not whether every advanced identity feature is enabled. It is whether the organisation has a clear answer to three questions: Who can administer the tenant? How are those accounts protected? How would we recover control?

Microsoft's current guidance distinguishes Security Defaults from Conditional Access. Security Defaults provide a simpler baseline, while Conditional Access can provide more granular policies when Microsoft Entra ID P1 or P2 is available. The important point is to choose a deliberate approach rather than leaving identity controls in an unknown state.

2. Treat administrator accounts differently

A common small-business weakness is giving one account every role because it is convenient. Convenience becomes a problem when that same account is used for ordinary email, web browsing and administration.

NorthWave's practical approach is to keep privileged access small, named and reviewable. Maintain a record of privileged roles, use lower-privileged accounts for normal work, and make sure there is a documented recovery path. Microsoft also recommends using roles with the fewest permissions necessary and treating Global Administrator as a highly privileged role.

3. Do not confuse Microsoft 365 with a complete backup strategy

Microsoft 365 provides resilience and recovery features, but a business should still define what data it needs to recover, how quickly it needs it and what its recovery process is. Accidental deletion, malicious activity, compromised accounts and business continuity requirements can all lead to different recovery needs.

Start by listing critical SharePoint sites, OneDrive data, mailboxes, Teams content and business documents. Then identify the recovery options available in the tenant and any independent backup service used by the business. Finally, test a realistic restore scenario and record the result.

The test matters. A backup or retention policy that has never been validated should not be described internally as “we can definitely restore everything”.

4. Review email protection and exceptions

Email is one of the most important Microsoft 365 security surfaces because it is both a communication system and a route into other services. Microsoft states that cloud mailboxes receive built-in protection, including quarantine for malware and high-confidence phishing. At the same time, business-specific exceptions can weaken protection if they are too broad.

Review mail-flow rules, allowed senders and domains, transport rules, forwarding arrangements and any third-party mail gateway. Each exception should have an owner and a reason. If nobody can explain why an exception exists, it deserves review.

Also review the domain itself. SPF, DKIM and DMARC should reflect the services that legitimately send mail on behalf of the business. This is particularly important when a company uses Microsoft 365 alongside a CRM, marketing platform, website forms or other cloud services.

5. Review sharing rather than trying to ban it

SharePoint, OneDrive and Teams are designed to make collaboration easy. The security objective is not to prevent collaboration; it is to make sharing understandable and proportionate to the data.

Ask where external sharing is allowed, who can create Teams or sites, whether guest accounts are reviewed and whether sensitive documents have additional controls. A business should also know who owns its important sites and what happens when the original owner leaves.

For smaller organisations, a short quarterly review of guest accounts and externally shared locations can be more useful than creating a complicated governance framework nobody maintains.

6. Turn audit data into something useful

Audit logging is valuable only if someone knows what to look for. Microsoft 365 can record user and administrator activity, but retention and available capabilities depend on the tenant and licence.

Define a small set of events worth investigating: unusual administrator changes, suspicious sign-ins, mailbox forwarding changes, unexpected sharing, creation of new privileged accounts and other activity relevant to the business. Document who investigates and what evidence should be preserved if an incident occurs.

This does not mean a small business needs a 24-hour security operations centre. It means that when something looks wrong, the organisation should have enough visibility to answer basic questions rather than starting from zero.

7. Use Secure Score intelligently

Microsoft Secure Score can provide recommendations and a useful view of security posture. It is a starting point for decisions, not a certificate that the tenant is “secure”. A higher score can be helpful, but a business should still understand the risk behind the recommendations.

For example, a recommendation may be irrelevant because a business does not use a particular feature, or it may already be addressed through another security product. Record those decisions rather than chasing points blindly.

8. Build a simple Microsoft 365 review record

A review becomes much more valuable when it can be repeated. A simple spreadsheet or service record can contain: review date, tenant owner, privileged accounts, MFA status, external sharing status, critical mail rules, audit status, recovery test date, major Secure Score recommendations and outstanding actions.

For each action, record an owner and target date. If the business decides not to make a change, record the reason and the risk accepted. This turns Microsoft 365 security from a one-off technical exercise into an operating process.

Where to start if you find gaps

• First: protect users and privileged identities with an appropriate MFA strategy.
• Second: review Global Administrator and other privileged roles.
• Third: confirm recovery information and test a realistic recovery scenario.
• Fourth: review email exceptions, forwarding and domain authentication.
• Fifth: review external sharing, guest access and important site ownership.
• Sixth: confirm audit visibility and turn useful Secure Score recommendations into an action plan.

This order keeps the review focused on controls that can materially affect account compromise, data exposure and recovery.

NorthWave view

The best Microsoft 365 security review is one a business can repeat.

Microsoft 365 is powerful enough that it can be tempting to treat the admin centre as a technical environment that only an IT specialist needs to understand. In practice, the most useful security improvements often start with ordinary business questions: who owns this system, who can access it, what happens when someone leaves, and how would we recover?

A small business does not need every advanced Microsoft security product to have sensible foundations. It needs deliberate identity protection, controlled privilege, sensible email and sharing configuration, useful visibility and a recovery plan that has been tested.

That is the purpose of this review: make the important decisions visible, assign ownership and revisit them as the business changes.