Cybersecurity Blog / Cloud Security
Microsoft 365 Security Baseline for Canadian Small and Mid-Sized Businesses
Microsoft 365 contains business-critical email, identities and files, making tenant security a central part of an organization's cyber risk. A useful baseline focuses first on preventing account takeover, limiting privilege, detecting suspicious activity and preserving the ability to investigate and recover.
1. Enforce strong multi-factor authentication
MFA should protect all users, with particular attention to administrators and high-value accounts. Avoid treating enrollment as the same thing as enforcement. Review exceptions and legacy authentication paths that can undermine MFA.
2. Use Conditional Access deliberately
Where licensing permits, Conditional Access can apply controls based on user, application, device and sign-in context. Policies should be tested carefully, include emergency access planning and avoid permanent exclusions that quietly become security gaps.
3. Reduce administrator privileges
Separate everyday user accounts from administrative identities where practical. Review Global Administrator and other privileged roles, remove unnecessary access and document who is authorized to make security-sensitive changes.
4. Harden email
Configure anti-phishing and impersonation protections appropriate to the organization. Review external forwarding, suspicious inbox rules and mailbox delegation. Implement and maintain SPF, DKIM and DMARC for domains used to send business email.
5. Protect SharePoint, OneDrive and Teams sharing
External collaboration is useful but should be governed. Review anonymous links, guest access, stale guests and overly broad sharing. Sensitive information should not become publicly accessible because of an easy-to-miss sharing setting.
6. Turn on useful auditing and alerting
Security logs are valuable only when they are available and someone knows how to use them. Define which events matter, such as risky sign-ins, privilege changes, suspicious mailbox behavior and unusual application consent. Establish who receives and investigates alerts.
7. Control third-party application access
OAuth and other integrations can gain access to Microsoft 365 data. Review enterprise applications and user consent, remove applications that are no longer required and restrict high-risk permissions.
8. Secure endpoints accessing Microsoft 365
Cloud security depends on endpoint security. Managed devices should use current operating systems, endpoint protection, disk encryption and reliable patching. Consider how unmanaged or personal devices are allowed to access sensitive information.
9. Prepare for compromised accounts
Document how to revoke sessions, reset credentials, investigate mailbox rules, review sign-in activity, remove malicious applications and communicate with affected users. Fast response matters because compromised accounts can be used for internal phishing and financial fraud.
10. Review the baseline regularly
Microsoft 365 changes continuously. New users, applications, policies and business requirements can create configuration drift. Schedule recurring security reviews and track remediation rather than relying on a one-time hardening project.
Need a Microsoft 365 security review?
The Cyber Arm can assess identity, email, sharing, administrative access and monitoring controls as part of a broader cybersecurity gap assessment.
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