SecurityInteractive Checklist

Microsoft 365 Security Checklist After Migration: 22 Steps to Lock Down Your Tenant

Most guides stop at "how to migrate." Nobody covers what to lock down after. This interactive checklist covers every critical security setting your new Microsoft 365 tenant needs.

May 9, 2026 15 min read Interactive Tool

You just migrated to Microsoft 365. Congratulations — but the work is not done. A freshly migrated tenant has default security settings that are not optimized for most businesses. Microsoft Secure Score for a new tenant typically starts at 30–40%. That means 60–70% of recommended security controls are not yet in place.

This interactive checklist covers 22 security steps across identity, email, data protection, device security, and monitoring. Work through it systematically and you will have a properly hardened Microsoft 365 environment.

Security Hardening Progress

0%0/22 complete

Critical: 0/5 doneNeeds attention

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Interactive Security Checklist

Identity & Access

0/6 complete

Enable Multi-Factor Authentication (MFA) for all usersCritical

Enable MFA for all admin accountsCritical

Set up Conditional Access policiesHigh

Review and remove legacy authentication protocolsHigh

Audit admin roles — remove unnecessary global adminsHigh

Enable Self-Service Password Reset (SSPR)Medium

Email Security

0/6 complete

Verify SPF record is updated to Microsoft 365Critical

Set up DKIM signing for your domainCritical

Configure DMARC policy (start with p=none, then p=quarantine)High

Enable Microsoft Defender for Office 365 (Safe Links + Safe Attachments)High

Configure anti-phishing policiesHigh

Enable anti-spam and anti-malware policiesMedium

Data Protection

0/4 complete

Configure Data Loss Prevention (DLP) policiesHigh

Set up Microsoft 365 Backup or third-party backupCritical

Review SharePoint external sharing settingsHigh

Configure retention policies for email and filesMedium

Device Security

0/3 complete

Enroll devices in Microsoft Intune (MDM)High

Enable Microsoft Defender for EndpointHigh

Configure device compliance policiesMedium

Monitoring & Alerts

0/3 complete

Enable Microsoft Secure Score and review recommendationsHigh

Set up alert policies for suspicious activityHigh

Enable audit loggingMedium

Understanding Microsoft Secure Score

Microsoft Secure Score is a measurement of your organization's security posture. It is available at security.microsoft.com and gives you a score out of 100 with prioritized recommendations.

0–40%

Needs Immediate Attention

Critical security gaps. Vulnerable to common attacks. Address MFA and email authentication immediately.

40–70%

Baseline Security

Core protections in place but advanced threats remain. Focus on Conditional Access and DLP policies.

70–100%

Well Secured

Strong security posture. Continue monitoring and address remaining recommendations as resources allow.

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Frequently Asked Questions: Microsoft 365 Security

QWhat are the most important Microsoft 365 security settings to configure after migration?

The top 5 most critical settings are: (1) Enable MFA for all users and admins, (2) Update SPF, DKIM, and DMARC DNS records, (3) Set up a third-party backup solution, (4) Configure anti-phishing and Safe Links/Safe Attachments policies, and (5) Review SharePoint external sharing settings. These five alone prevent the vast majority of Microsoft 365 security incidents.

QIs Microsoft 365 secure out of the box?

Microsoft 365 has reasonable default security settings, but they are not optimized for most businesses. Key features like MFA, DKIM, DMARC, Conditional Access, and DLP policies require manual configuration. Microsoft Secure Score typically starts at 30–40% for a new tenant — our checklist helps you get to 70%+ which is the recommended baseline.

QDo I need Microsoft 365 Business Premium for security features?

Some security features require Business Premium ($22/user/month): Microsoft Defender for Business, Intune device management, Conditional Access, and Azure AD Plan 1. However, many critical features are available in all plans: MFA, SPF/DKIM/DMARC, anti-spam, anti-malware, and audit logging. Start with what you have and upgrade if your security requirements demand it.

QHow do I check my Microsoft 365 security score?

Go to security.microsoft.com and click "Secure Score" in the left navigation. Your score is shown as a percentage with a breakdown of completed and recommended actions. Each action shows the impact on your score and step-by-step instructions. Aim for 70%+ as a baseline for small businesses, 80%+ for regulated industries.

QWhat is the biggest Microsoft 365 security risk after migration?

The biggest risk is leaving legacy authentication protocols enabled. Basic Auth (used by older email clients and IMAP/POP3 without modern auth) bypasses MFA entirely. Attackers specifically target these protocols because they can brute-force passwords without triggering MFA. Block Basic Auth in Exchange Online as a top priority.

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