Microsoft 365 Security Best Practices for Businesses
Microsoft 365 is the productivity backbone of most businesses in Greater Sudbury and Parry Sound, but the default tenant configuration leaves significant gaps. This guide walks through the Microsoft 365 security controls every business should review, with specific settings to enable and common mistakes to avoid.
Lock down identity first
Enforce multi-factor authentication
Enable MFA for every licensed user, not just administrators. Use the Microsoft Authenticator app with number-matching where possible SMS codes are better than nothing but can be intercepted.
Use Conditional Access
Conditional Access policies (available in Microsoft 365 Business Premium and most Enterprise plans) let you require MFA, block sign-ins from risky locations, and force managed devices for accessing sensitive resources.
Protect admin accounts
- Use dedicated admin accounts separate from daily-use mailboxes
- Require phishing-resistant MFA for Global Administrators
- Limit Global Admin assignments to two or three named individuals
Harden Exchange Online and email
- Enable Microsoft Defender for Office 365 Safe Links and Safe Attachments
- Configure anti-phishing impersonation protection for executives and the company domain
- Disable legacy authentication protocols (POP, IMAP, Basic Auth) tenant-wide
- Publish SPF, DKIM, and DMARC records, then move DMARC policy from p=none to p=quarantine or p=reject
- Set up external-sender mail tips so staff can spot impersonation
Protect data in SharePoint, OneDrive, and Teams
- Restrict external sharing to authenticated guests only
- Enable sensitivity labels for confidential documents
- Configure retention policies for legal and compliance obligations
- Turn off anonymous link sharing unless absolutely required
Back up Microsoft 365 properly
Microsoft's shared responsibility model means YOU are responsible for protecting your data from accidental deletion, malicious deletion, and ransomware. Native retention is not a backup. Use a dedicated Microsoft 365 backup product that covers Exchange mailboxes, OneDrive, SharePoint, and Teams data with point-in-time restore.
Monitor and review
- Check Microsoft Secure Score monthly and remediate the top recommendations
- Enable mailbox audit logging and review sign-in logs for anomalies
- Run quarterly access reviews for guest accounts and admin roles
Frequently asked questions
Is Microsoft 365 Business Basic enough for security?
Business Basic includes the core productivity apps but lacks Defender for Office 365, Intune, and Conditional Access. Business Premium is the recommended baseline for most small Ontario businesses.
Does Microsoft back up my data?
No. Microsoft replicates data for service availability but does not protect against user deletion, ransomware, or malicious insiders. You must use a third-party Microsoft 365 backup.
What is Microsoft Secure Score?
Microsoft Secure Score is a 0-100 measurement of your tenant's security posture, with prioritized recommendations. Most unmanaged tenants score under 30%. A properly hardened SMB tenant typically lands in the 60-80% range.
Need help hardening your Microsoft 365 tenant?
We perform Microsoft 365 security reviews for Ontario businesses and implement a documented hardening plan.
Technologies mentioned in this article
See what we support around each platform on our supported technologies hub.
Related services, locations, and resources
Related services
- Cybersecurity Services
Endpoint protection, MFA, email filtering, and M365 hardening.
- Microsoft 365 Support
Exchange, Teams, SharePoint, OneDrive, and licensing.
- Managed IT Services
Proactive monitoring, patching, and predictable monthly support.
- Backup & Disaster Recovery
Backup strategy, monitoring, and recovery testing.
Related service areas
Related resources
- Common Microsoft 365 Security Mistakes (and How to Fix Them)
Ten Microsoft 365 misconfigurations we routinely find during tenant audits for Northern Ontario businesses …
- IT Onboarding Checklist for New Employees
A practical IT onboarding checklist for new hires: accounts, MFA, device setup, security, permissions, Micr…
- IT Offboarding Checklist: What to Do When an Employee Leaves
A step-by-step IT offboarding checklist for when an employee leaves: disable sign-in, revoke sessions, reta…
- Why Does Outlook Keep Crashing?
Outlook is the most common ticket a Sudbury MSP sees. Here are the real reasons it crashes on business PCs …