Office 365 Security Best Practices Every MSP Should Follow

Why MSPs Must Lead on Microsoft 365 Security

Your clients trust you with their technology stack. For most small and mid-size businesses, that stack runs on Microsoft 365. The problem is that M365 defaults are designed for ease of use, not security. As an MSP, you are the front line of defense — and the one your clients will blame when something goes wrong.

Following proven security best practices across every tenant you manage is not optional. It is the foundation of your service delivery and your reputation.

Enforce MFA Across Every Tenant — No Exceptions

Multi-Factor Authentication is the single most effective control you can deploy. Microsoft reports that MFA blocks 99.9% of account compromise attacks.

What to do:

• Enable Conditional Access-based MFA (not per-user MFA, which is being deprecated)
• Block legacy authentication protocols that cannot support MFA
• Use number matching and additional context in Microsoft Authenticator to prevent MFA fatigue attacks
• Create a break-glass emergency access account with MFA but excluding Conditional Access, stored securely

Common MSP mistake: Excluding themselves or the client’s C-suite from MFA policies. Every account needs MFA, especially privileged ones.

Standardize Security Baselines Across Clients

Consistency saves time and reduces risk. Develop a standard security configuration that you apply to every new tenant.

Your baseline should include:

• Conditional Access policies (MFA, device compliance, location restrictions, sign-in risk)
• Exchange Online Protection settings (anti-phishing, anti-spam, Safe Links, Safe Attachments)
• SharePoint/OneDrive sharing restrictions (no anonymous links, expiration on guest access)
• Teams governance (app permissions, guest access, meeting policies)
• Audit logging enabled with extended retention
• Alert policies for suspicious activity

Pro tip: Document your baseline in a runbook. This makes onboarding new technicians faster and ensures nothing gets missed during client onboarding.

Lock Down Email — It Is Still the Top Attack Vector

Phishing and business email compromise (BEC) account for billions in losses annually. Every client tenant needs robust email security.

Critical email security steps:

• Configure SPF, DKIM, and DMARC for every client domain (aim for DMARC p=reject)
• Enable anti-phishing policies with impersonation protection for executives
• Block auto-forwarding to external domains (this is a common exfiltration method)
• Review mail flow rules quarterly for suspicious forwarding or filtering bypass rules
• Implement Safe Links and Safe Attachments if licensing allows (Defender for Office 365 Plan 1 or Business Premium)

Manage Privileged Access Like It Matters

Because it does. A compromised Global Admin account means game over.

Privileged access best practices:

• Limit Global Admins to 2-4 per tenant (use role-based admin roles for specific tasks)
• Enable Privileged Identity Management (PIM) for just-in-time admin access
• Use dedicated admin accounts separate from daily-use accounts
• Review admin role assignments quarterly
• Set up alerts for new admin role assignments

Monitor and Alert Proactively

Your clients are not watching their M365 security dashboards. You need to be.

Key monitoring activities:

• Set up Microsoft 365 alert policies for impossible travel, mass downloads, and new forwarding rules
• Review Microsoft Secure Score monthly for each tenant
• Check sign-in logs for failed attempts and risky sign-ins
• Monitor for new inbox rules created via PowerShell (a BEC indicator)
• Track changes to Conditional Access policies and admin roles

Conduct Regular Security Assessments

Point-in-time audits catch configuration drift, new risks, and settings that changed since the last review. The challenge is doing this efficiently across all your clients.

Assessment cadence recommendations:

• Full security assessment: quarterly
• Secure Score review: monthly
• Critical setting verification (MFA, forwarding rules, admin accounts): weekly
• Compliance check (for regulated industries): quarterly or per regulatory requirements

Scale Your Assessments With Automation

Running manual PowerShell scripts across dozens of tenants does not scale. This is exactly why we built 365 Security Assessment — to give MSPs and MSSPs a way to run forensic-level M365 audits in minutes.

The platform checks over 11,000 data points per tenant, maps findings to MITRE ATT&CK, and produces branded PDF reports you can present to clients. It is 100% read-only and designed for multi-tenant MSP workflows.

Start your free assessment and see your first client report in under 10 minutes.