Microsoft 365 Security Insight
10 Microsoft 365 Security Settings Every Business Should Enable
A practical security-hardening guide for Australian businesses using Microsoft 365, covering identities, email, devices, data and administrator access.
Every organisation should start by protecting identities with multifactor authentication, controlling access with Conditional Access, reducing privileged access, strengthening email protection, securing endpoints, blocking legacy authentication and monitoring security alerts. The exact configuration should be tested against business requirements before broad deployment.
Why Microsoft 365 Security Settings Matter
Microsoft 365 sits at the centre of many businesses. It commonly contains email, files, calendars, identities, collaboration data and access to connected applications. That makes the tenant an attractive target for phishing, credential theft, business email compromise and ransomware.
Microsoft provides a broad set of built-in controls, but many of them still require planning and configuration. A licence may make a capability available without automatically applying the most appropriate policy to every user and device.
Important implementation note
Security controls can interrupt legitimate access when they are deployed without testing. Use pilot groups, document exceptions, maintain emergency access accounts and prepare rollback steps before enforcing major tenant-wide changes.
1. Require Multifactor Authentication
Multifactor authentication, commonly called MFA, requires a user to provide more than a password when signing in. This makes a stolen or guessed password less useful to an attacker.
Security defaults can provide a straightforward baseline for smaller or simpler environments. Organisations with Microsoft Entra ID Premium P1 or P2 licensing can use Conditional Access for more granular enforcement.
Recommended approach
- Require MFA for every user, including administrators.
- Prefer stronger authentication methods over SMS where practical.
- Register at least two approved methods for critical administrators.
- Review authentication method registration and remove obsolete methods.
- Keep tightly controlled emergency access accounts for recovery scenarios.
2. Use Conditional Access Policies
Conditional Access evaluates signals such as the user, device, application, location and sign-in context before access is granted. It allows an organisation to move beyond a single rule applied identically to every sign-in.
Microsoft 365 Business Premium includes Microsoft Entra ID Premium P1 capabilities, which support Conditional Access.
Useful baseline policies
- Require MFA for all users.
- Require stronger controls for administrator roles.
- Block legacy authentication.
- Require compliant or approved devices for sensitive applications.
- Control access from unsupported platforms or high-risk locations.
- Use report-only mode before enforcement where available.
Avoid accidental lockout
Exclude carefully protected emergency access accounts from normal Conditional Access policies, monitor their use and test every policy with a limited pilot group before enabling it for the whole organisation.
3. Block Legacy Authentication
Legacy authentication protocols do not support modern security controls in the same way as modern authentication. Where they remain available, they can create a path around MFA and other access protections.
Before blocking legacy authentication, identify old mail clients, multifunction devices, line-of-business applications and service accounts that may still depend on it. Replace or reconfigure those dependencies rather than leaving broad exceptions in place.
What to review
- Older versions of Outlook and other email clients.
- POP, IMAP and SMTP authentication requirements.
- Printers and scanners sending email.
- Applications using basic username-and-password authentication.
- Service accounts with undocumented sign-in dependencies.
4. Protect Administrator Accounts
Administrator accounts can change security settings, access sensitive data and create additional privileged accounts. They therefore require stronger protection than ordinary user accounts.
Recommended controls
- Use separate accounts for administration and everyday work.
- Assign the least-privileged role required for each task.
- Limit the number of Global Administrators.
- Require phishing-resistant authentication for privileged roles where possible.
- Review privileged role assignments regularly.
- Do not use administrator accounts for email, browsing or routine collaboration.
A small business may not need a complex privileged-access programme, but it should still know exactly who has elevated permissions and why.
5. Apply Microsoft Defender Email Protection
Email remains one of the most common entry points for attacks. Microsoft 365 includes anti-spam and anti-malware protections, and eligible licences provide additional Defender for Office 365 capabilities such as Safe Links and Safe Attachments.
Microsoft recommends using its Standard or Strict preset security policies as a practical way to apply recommended protection settings. The correct policy should be piloted and adjusted for legitimate business workflows.
Settings to review
- Anti-phishing and impersonation protection.
- Safe Links for supported email and collaboration workloads.
- Safe Attachments and dynamic file analysis.
- Anti-spam and outbound spam policies.
- Quarantine policies and user notification settings.
- Protection for high-value users such as executives and finance staff.
6. Configure Microsoft Defender for Business
Microsoft Defender for Business provides endpoint security capabilities for eligible small and medium businesses. It can support antivirus, endpoint detection and response, vulnerability visibility and automated investigation.
The service should be deployed to supported business devices and monitored rather than treated as a passive licence entitlement.
Key areas to configure
- Onboard all supported company endpoints.
- Enable cloud-delivered protection and automatic sample submission.
- Review next-generation protection and firewall policies.
- Enable appropriate attack surface reduction rules.
- Configure web protection and controlled folder access where suitable.
- Set alert notifications and assign responsibility for incident response.
7. Enforce Device Compliance with Microsoft Intune
Microsoft Intune allows businesses to manage supported devices, applications and security policies. Device compliance can also be combined with Conditional Access so that sensitive services are not available from devices that fail defined requirements.
Common compliance requirements
- Supported operating-system version.
- Encryption enabled.
- Firewall and antimalware active.
- No simple passwords or unsupported device states.
- Device risk below the organisation's chosen threshold.
- Defined grace periods and remediation instructions.
Compliance rules should reflect genuine business risk. Policies that are too weak provide little protection, while policies that are too aggressive can create unnecessary support incidents.
8. Restrict External Sharing and Guest Access
SharePoint, OneDrive and Microsoft Teams make collaboration easy, including collaboration with people outside the organisation. That flexibility needs guardrails to reduce accidental or excessive sharing.
Recommended review points
- Define who is allowed to invite guests.
- Set appropriate SharePoint and OneDrive sharing levels.
- Use links that require authentication for sensitive information.
- Apply expiry periods where practical.
- Review inactive guests and external sharing regularly.
- Use sensitivity labels or restricted sites for high-risk content.
9. Use Sensitivity Labels and Data Loss Prevention
Microsoft Purview information-protection capabilities can help identify, classify and protect sensitive information. Business Premium includes capabilities such as sensitivity labels, message encryption and eligible data loss prevention controls.
Start with a simple classification model that employees can understand. Too many labels or unclear rules often reduce adoption.
A practical starting point
- Create a small number of clearly named sensitivity labels.
- Define what information belongs in each category.
- Apply encryption or sharing restrictions only where justified.
- Introduce DLP rules in test or audit modes before blocking activity.
- Train users so labels are meaningful rather than administrative noise.
10. Enable Auditing, Alerts and Regular Security Reviews
Prevention controls are only part of security. Businesses also need visibility into suspicious activity and a repeatable process for reviewing alerts, configurations and access.
Operational actions
- Confirm audit logging and required retention are available.
- Configure alert notifications for the responsible people or provider.
- Review Microsoft Defender incidents and recommendations.
- Monitor unusual administrator activity and mailbox changes.
- Review Secure Score as a prioritisation aid, not as the sole measure of security.
- Schedule recurring access, device and security-policy reviews.
A security alert that nobody sees or owns provides limited value. Every organisation should define who investigates alerts, how quickly they respond and when an incident is escalated.
Microsoft 365 Security Settings Priority Table
| Security control | Primary risk reduced | Suggested priority |
|---|---|---|
| Multifactor authentication | Stolen or guessed passwords | Immediate |
| Conditional Access | Inappropriate or high-risk access | Immediate |
| Block legacy authentication | Bypassing modern authentication controls | Immediate |
| Administrator protection | Privileged account compromise | Immediate |
| Email protection policies | Phishing, malware and impersonation | High |
| Defender for Business | Endpoint compromise and ransomware | High |
| Intune compliance | Access from insecure or unmanaged devices | High |
| External sharing controls | Data leakage and unmanaged guest access | High |
| Labels and DLP | Accidental handling of sensitive information | Planned rollout |
| Auditing and alert review | Delayed detection and response | Immediate |
A Practical Microsoft 365 Security Implementation Plan
Phase 1: Discover
- Inventory users, administrators, devices, applications and licences.
- Identify legacy authentication and service-account dependencies.
- Review existing security policies and known exceptions.
- Confirm who owns security alerts and tenant administration.
Phase 2: Protect identities
- Register and enforce MFA.
- Separate administrative and everyday accounts.
- Build and test Conditional Access policies.
- Block legacy authentication once dependencies are addressed.
Phase 3: Protect email and devices
- Apply appropriate preset email-security policies.
- Onboard devices to Defender for Business.
- Deploy Intune security and compliance policies through pilot groups.
- Connect device compliance to Conditional Access where appropriate.
Phase 4: Protect data and operate
- Review external sharing and guest access.
- Introduce sensitivity labels and DLP gradually.
- Configure alerts, reporting and incident-response responsibilities.
- Schedule ongoing reviews and policy maintenance.
Frequently Asked Questions
What is the most important Microsoft 365 security setting?
MFA is one of the most important controls because it reduces the risk that a stolen password alone can be used to access an account. Organisations with suitable licensing should generally enforce it through carefully designed Conditional Access policies.
Are Microsoft 365 security settings enabled automatically?
Some protections are enabled by default, but many advanced controls require configuration, testing and ongoing review. Buying a licence does not automatically deploy every available security feature.
Does Microsoft 365 Business Premium include Conditional Access?
Yes. Business Premium includes Microsoft Entra ID Premium P1 capabilities, including Conditional Access.
Does Microsoft 365 Business Premium include endpoint security?
It includes Microsoft Defender for Business and Microsoft Intune capabilities that can be used to protect and manage supported endpoints.
Should every organisation use the same security policies?
No. The core control areas are broadly applicable, but the detailed settings should reflect the organisation's users, devices, applications, risk profile and operational needs.
Official Microsoft References
Microsoft 365 services and licensing can change. Confirm current capabilities and implementation guidance before deployment.
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