Microsoft 365 Security Best Practices: Protecting Your Cloud Workspace

# Microsoft 365 Security Best Practices: Protecting Your Cloud Workspace

Microsoft 365 is the most widely used business productivity platform in the world — which also makes it the most widely attacked. A default M365 deployment is not secure. Every organization needs to harden their configuration beyond out-of-the-box defaults.

## The Non-Negotiable Controls

These are baseline security settings that every M365 tenant should have enabled. If any of these are missing in your environment, address them immediately.

### 1. Multi-Factor Authentication (MFA)

MFA blocks 99.9% of automated attacks. Enable it for every user — no exceptions.

### 2. Conditional Access

Beyond basic MFA, Conditional Access policies control how and where your users can sign in:

### 3. Email Security

Email is the primary attack vector for business compromise:

• **Exchange Online Protection (EOP)** — Verify it is configured with recommended settings
• **Safe Attachments** — Scan email attachments in a sandbox before delivery
• **Safe Links** — Rewrite and scan URLs in emails at time-of-click
• **Anti-phishing policies** — Enable mailbox intelligence, impersonation protection
• **DMARC, DKIM, SPF** — Configure all three DNS records for email authentication
• **External email warning** — Add a banner to emails from outside the organization

### 4. Data Loss Prevention (DLP)

Prevent sensitive data from leaving your organization: - Create DLP policies for credit card numbers, Social Security numbers, health records - Apply policies to Exchange, SharePoint, OneDrive, and Teams - Start with audit-only mode to understand data patterns before enforcing blocks

### 5. SharePoint and OneDrive Security

• Disable anonymous sharing links (or restrict to view-only with expiration)
• Require authentication for external sharing
• Enable versioning on all document libraries (ransomware recovery)
• Set sharing defaults to "People in your organization" (not "Anyone with the link")

## Advanced Controls

### Admin Account Separation

• Global administrators should use dedicated admin accounts — never their daily-use accounts
• Admin accounts should not have email licenses (reduces phishing attack surface)
• Limit the number of Global Admins to 2-4 maximum
• Use Privileged Identity Management (PIM) for just-in-time admin access

### Audit Logging

• Enable Unified Audit Log (it may not be on by default)
• Set log retention to 90 days minimum (365 days with E5 license)
• Configure alerts for suspicious activities: mass file deletion, mail forwarding rules, permission changes
• Review audit logs regularly or send to a SIEM for automated monitoring

### Mobile Device Management

If employees access M365 from mobile devices: - Deploy Intune MAM (Mobile App Management) policies at minimum - Require PIN or biometric to open M365 apps - Prevent copy/paste from M365 apps to personal apps - Enable remote wipe for corporate data on personal devices

## Microsoft Secure Score

Microsoft provides a built-in security posture score at security.microsoft.com: - Review your current score and recommended improvements - Prioritize improvements by impact and implementation effort - Target: Score above 75% (most organizations start around 30-40%) - Review monthly and address new recommendations

## Common Misconfigurations

## Quick-Win Implementation Order

Summit DNC manages Microsoft 365 security for businesses across Southern California. We harden your tenant configuration, deploy advanced protection, and monitor for threats — so you get the productivity benefits of M365 without the security risk of default settings. Contact us for a Microsoft 365 security audit.