Securing a Microsoft 365 Tenant
After Migration

Multi-factor authentication — the highest-priority item

If MFA wasn't enabled before or during migration, it needs to be the first thing addressed afterward. A tenant with password-only authentication is exposed to credential-stuffing and phishing attacks regardless of anything else configured correctly. Microsoft 365 supports several enforcement methods — per-user MFA, security defaults, or Conditional Access-based MFA — and the right choice depends on the organisation's size and existing Conditional Access maturity.

For smaller tenants without existing Conditional Access policies, Microsoft's security defaults provide a reasonable baseline with minimal configuration. For larger organisations, Conditional Access-based MFA is preferable because it allows more nuanced policies — for example, requiring MFA for external or high-risk sign-ins while reducing friction for trusted, compliant devices on the corporate network.

Conditional Access — moving beyond all-or-nothing security

Conditional Access policies let you apply security requirements based on context: the user's location, the device's compliance state, the application being accessed, and the assessed risk level of the sign-in. Rather than a blanket rule applied identically to every user and scenario, Conditional Access lets policy match risk — stricter requirements for access to sensitive data or from unmanaged devices, lighter friction for low-risk, routine access.

Common policies worth establishing early include blocking legacy authentication protocols (which don't support MFA and are a common attack vector), requiring compliant or hybrid-joined devices for access to sensitive applications, and requiring MFA for any sign-in from outside expected geographic locations. These are not exotic configurations — they are baseline hardening steps appropriate for almost every organisation.

Microsoft Defender configuration

Microsoft 365's Defender suite — spanning email protection, endpoint protection, and identity protection depending on licensing tier — is frequently left in its default configuration after migration, which is adequate but not optimised. Anti-phishing policies, safe attachments, and safe links protections should be reviewed and tuned specifically for the organisation's risk profile rather than left at Microsoft's out-of-box defaults, which are designed to be broadly reasonable rather than specifically appropriate for any one organisation.

For organisations that migrated from a GoDaddy-managed tenant specifically, this step matters more than usual — Defender configuration is one of the areas most commonly restricted under GoDaddy's management layer, meaning many of these settings may never have been properly configured at all before defederation. See our guide on GoDaddy Microsoft 365 limitations for the broader context on what's typically been unavailable.

Admin role hygiene and least privilege

Migrations often result in more people holding Global Administrator access than actually need it — sometimes because it was the simplest way to grant necessary access mid-project, and the reduction never happened afterward. Microsoft 365 supports granular admin roles (Exchange Administrator, SharePoint Administrator, User Administrator, and dozens of others) that should be used instead of blanket Global Administrator access wherever the specific role covers what's needed.

Two related practices are worth establishing at this point: Privileged Identity Management (PIM), if licensing supports it, to make admin access time-bound and require justification rather than standing permanently active; and at least one "break-glass" emergency access account, excluded from Conditional Access policies and stored securely, to prevent a misconfigured policy from locking every administrator out simultaneously.

Data Loss Prevention and sensitive information handling

Once data has moved into Microsoft 365, Data Loss Prevention (DLP) policies can identify and restrict sharing of sensitive information — financial data, personal information, credentials — based on content inspection rather than relying on users to manually classify or restrict what they share. This is genuinely more achievable post-migration than it typically was in a legacy on-premise or GoDaddy-managed environment, since DLP is one of the Microsoft 365 features most commonly unavailable under restricted management.

Audit logging and alerting

Microsoft 365's unified audit log captures activity across Exchange, SharePoint, and Teams, but it needs to be enabled and retained appropriately — and alerting policies need to be configured to actually surface anomalous activity rather than relying on someone manually reviewing logs. Suspicious sign-in alerts, mass file download alerts, and mailbox forwarding rule alerts are common starting points that catch a meaningful share of real security incidents without requiring a dedicated security operations function.

Putting this in order

Not everything needs to happen on day one. A reasonable sequence for most organisations is: MFA and basic Conditional Access in the first week, Defender policy review in the first month, admin role cleanup and PIM within the first quarter, and DLP and audit alerting as an ongoing refinement. Treating this as a structured rollout rather than an all-at-once project makes it achievable without disrupting users who are already adjusting to a new environment post-migration.

This is distinct from — and comes after — the operational checklist covered in our Microsoft 365 migration checklist, which focuses on the migration project itself rather than ongoing tenant security posture.

CloudyNex's migration consulting service includes post-migration security review as part of a broader independent assessment, and our project management service can structure this rollout as a defined phase following the migration itself.