Microsoft 365 Security Hardening: The Complete MSP Configuration Guide
M365 is the most common platform MSPs manage. This guide covers the critical security configurations that most MSPs miss during client deployments.
Microsoft 365 is the single most common platform in MSP client environments, yet the default security configuration leaves significant gaps. Microsoft's out-of-the-box settings prioritize usability over security, which means every new M365 tenant needs hardening before it's production-ready. Many MSPs have a mental checklist of settings to configure, but without a documented, standardized baseline, critical settings get missed — especially as Microsoft continually adds new features and security controls across their rapidly evolving platform.
Identity and Access Hardening
Start with Entra ID (formerly Azure AD) security defaults or, better yet, Conditional Access policies that enforce MFA for all users with risk-based step-up authentication. Disable legacy authentication protocols that bypass MFA — this single change blocks a huge percentage of credential attacks. Implement Privileged Identity Management to provide just-in-time access for administrative roles rather than standing privileges. Block sign-ins from countries where you have no business operations. Configure session timeouts and reauthentication requirements for sensitive applications. Disable user consent for third-party applications — this prevents OAuth phishing attacks where users unknowingly grant attackers access to their mailboxes and files by approving a malicious app consent prompt.
Email and Data Protection
Configure Exchange Online Protection with aggressive anti-phishing policies: enable impersonation protection for executives and high-value targets, configure spoofing intelligence, and implement Safe Links and Safe Attachments across the tenant. Deploy DMARC, DKIM, and SPF to prevent email spoofing of your client's domains — and set DMARC to reject, not just quarantine. Enable audit logging in the Microsoft Purview compliance portal and ensure logs are retained for at least one year. Configure Data Loss Prevention policies to detect and prevent the sharing of sensitive information like credit card numbers, Social Security numbers, and health records. Finally, implement sensitivity labels for document classification and encryption, giving users the tools to protect sensitive files without changing their workflow. Review your configuration against CIS Microsoft 365 Benchmarks quarterly to catch new recommendations.