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Microsoft 365 Security Checklist for Small Businesses
Microsoft 365 defaults favor easy setup over protection. These are the settings worth checking first.
Updated June 2026 · 7 min read
Microsoft 365 is a capable security platform, but out of the box it is configured for quick onboarding rather than strong protection. Most small business risk comes from a handful of settings that were never changed. This checklist walks the areas that matter most for a 10 to 75 person company.
Identity and access
- Require multi-factor authentication for every user, including owners and executives.
- Block legacy authentication, which attackers use to bypass MFA.
- Limit the number of Global Administrators and use separate admin accounts.
- Where licensed, use Conditional Access to control risky sign-ins and locations.
- Publish SPF, DKIM, and DMARC for your domain to reduce spoofing.
- Turn on anti-phishing and safe-link protection.
- Disable automatic external forwarding, a common path for quiet data theft.
- Add external sender tagging so staff can spot impersonation.
Data and sharing
- Review SharePoint and OneDrive external sharing. Default sharing is often broader than owners expect.
- Check anonymous link settings and expiration.
- Know where your sensitive files live and who can reach them. Our SharePoint security work covers this.
Devices
- Use endpoint detection and response on company devices, not consumer antivirus.
- Where licensed, enroll devices so you can enforce encryption and remove access from lost hardware.
Monitoring and backup
- Confirm the audit log is on so you can investigate later.
- Add a third-party backup for Microsoft 365. The platform is not a backup, and recovery is your responsibility.
- Test a restore on a schedule, not only when something breaks.
Where to start
If you only do three things, require MFA everywhere, block legacy authentication, and add a tested backup. From there, a Tecnico Ready security review gives you a prioritized list specific to your tenant, and Microsoft 365 security services covers ongoing hardening.
Key takeaways
- Microsoft 365 is not secure by default. The defaults favor easy setup.
- MFA for all users plus blocking legacy authentication is the highest-impact change.
- Microsoft 365 is not a backup. Add one and test restores.
- External sharing is usually broader than owners realize. Review it.
Microsoft 365 security questions
Is Microsoft 365 secure by default?
No. Microsoft 365 gives you strong security tools, but the default settings are built for easy setup, not maximum protection. Identity, email, and sharing settings usually need to be tightened.
Does Microsoft 365 back up my data?
Not in the way most people assume. Microsoft keeps the service running and offers limited retention, but recovering data after accidental deletion, a ransomware event, or a departed employee is your responsibility. A separate backup is recommended.
What is the single most important Microsoft 365 security setting?
Multi-factor authentication for every user, with legacy authentication blocked. It prevents the large majority of account takeover attempts and is also a common cyber insurance requirement.
Do I need Microsoft 365 Business Premium for good security?
Business Premium adds valuable controls such as Conditional Access and device management, but you can improve security on lower plans too. The right plan depends on your size, risk, and budget, which is what a review helps decide.
See where your Microsoft 365 stands
Book a Security Fit Call and we will walk the settings that matter most for your tenant.