How to Prepare for a Microsoft 365 Migration: 2026 Complete Guide

A successful Microsoft 365 migration in 2026 is not only a mailbox or file move. It is an identity, security, licensing, compliance, endpoint, and adoption project that should leave your organization cleaner, safer, and easier to manage than before.

Start with a Migration Readiness Assessment

Before moving data, document what you have, what you will keep, what you will archive, and what must change. Inventory users, groups, domains, mailboxes, shared mailboxes, distribution lists, Microsoft Teams, SharePoint sites, OneDrive accounts, Power Platform assets, line-of-business integrations, devices, security policies, and third-party applications. Confirm business constraints such as blackout dates, legal holds, retention requirements, executive users, regional data residency needs, and acceptable downtime. A readiness assessment should produce a migration scope, risk register, workload-by-workload plan, rollback approach, and stakeholder communication plan.

Modernize Identity with Microsoft Entra ID

Microsoft Entra ID is central to a secure Microsoft 365 migration. Review user principal names, proxy addresses, duplicate accounts, guest accounts, stale accounts, privileged roles, authentication methods, and directory synchronization. If you use hybrid identity, validate Microsoft Entra Connect Sync or Microsoft Entra Cloud Sync configuration before cutover. Enable or enforce multifactor authentication, prepare Conditional Access policies, and document break-glass accounts. For tenant-to-tenant scenarios, plan identity matching, cross-tenant access settings, B2B collaboration, domain release timing, and any required coexistence. Use least privilege for migration admin accounts and remove temporary permissions after the project.

Plan Security and Microsoft Purview Compliance Early

Replace legacy compliance planning with Microsoft Purview planning. Before migration, decide how you will handle sensitivity labels, retention labels and policies, Data Loss Prevention, eDiscovery, audit logging, records management, insider risk requirements, and data lifecycle rules. Review Microsoft Secure Score, Defender for Office 365 policies, anti-phishing settings, safe links, safe attachments, external sharing controls, and privileged access. If the migration includes sensitive SharePoint or OneDrive content, clean up overshared sites and anonymous links before users start relying on Microsoft 365 Copilot or expanded search experiences.

Right-Size Licensing Under CSP and New Commerce Experience

Licensing should be planned before migration, not fixed afterward. Map licenses to real personas such as frontline workers, knowledge workers, executives, shared-device users, and administrators. Under Microsoft’s Cloud Solution Provider and New Commerce Experience models, review monthly versus annual commitments, renewal dates, limited cancellation windows, add-ons, security and compliance plans, audio conferencing or Teams Phone needs, and regional differences in Microsoft Teams licensing where applicable. Build a license assignment strategy using groups where possible, reclaim unused licenses after cutover, and monitor utilization regularly so the tenant does not accumulate unnecessary cost.

Prepare Each Microsoft 365 Workload

Exchange Online preparation should include accepted domains, DNS, mail flow, connectors, shared mailboxes, public folders if applicable, mailbox permissions, litigation hold, retention, transport rules, and message trace validation. SharePoint Online and OneDrive preparation should include site inventory, storage planning, permission cleanup, external sharing review, versioning, retention, and migration mapping. Teams preparation should include teams, channels, private and shared channels, meeting policies, calling requirements, apps, tabs, and governance. Power Platform preparation should include environments, connectors, data loss prevention policies, ownership, and business-critical flows. Do not overlook Entra enterprise applications, certificates, secrets, SSO integrations, and line-of-business dependencies.

Tenant-to-Tenant Migration Checklist for 2026

Tenant-to-tenant migrations require more planning than standard onboarding because identity, domains, workloads, and user experience all change at once. Document the source and target tenants, verify ownership of domains, decide when each domain will be released and added, and plan coexistence if users must collaborate across tenants during the transition. Prepare identity matching, mailbox migration batches, OneDrive and SharePoint mapping, Teams migration expectations, guest access, Entra applications, Power Platform assets, device enrollment impact, and DNS cutover. Microsoft native capabilities such as cross-tenant mailbox migration may fit some Exchange scenarios, while complex Teams, SharePoint, OneDrive, or coexistence requirements often require specialized third-party tooling. Always run pilot migrations before moving executives or high-risk departments.

Use the Right Migration Tools

Choose tooling based on workload complexity, coexistence needs, compliance requirements, and timeline. Microsoft-native options may include Exchange migration methods, hybrid configurations, cross-tenant mailbox migration where appropriate, SharePoint Migration Tool, Migration Manager, OneDrive known folder move, and FastTrack assistance where the customer and workload are eligible under current Microsoft terms. Third-party migration platforms can be valuable for complex tenant-to-tenant projects, advanced reporting, Teams content migration, coexistence, throttling management, and granular scheduling. Validate tooling with pilot users, test permissions and metadata, and confirm how failures, retries, and delta passes are handled.

Include Microsoft Intune and Endpoint Readiness

Endpoint management is a major success factor. Use Microsoft Intune to prepare device enrollment, compliance policies, configuration profiles, endpoint security baselines, app deployment, app protection policies, BitLocker, Microsoft Defender for Endpoint integration, and remote actions such as wipe, retire, reset, and sync. For new or rebuilt Windows devices, plan Windows Autopilot. For bring-your-own-device scenarios, consider mobile application management without full device enrollment where appropriate. Organizations with advanced endpoint needs should evaluate Microsoft Intune Suite capabilities such as Endpoint Privilege Management and advanced endpoint analytics based on licensing and business requirements.

Prepare for Microsoft 365 Copilot Readiness

If Microsoft 365 Copilot is planned now or later, migration is the right time to improve data hygiene. Review SharePoint and OneDrive permissions, overshared content, guest access, unmanaged sites, stale files, sensitivity labels, retention, and data classification. Confirm licensing prerequisites and identity/security controls before assigning Copilot licenses. Copilot readiness is not only a license decision; it depends on clean permissions, governed content, secure collaboration, and user training.

Communicate, Train, and Support Users

Create a communication plan that explains what is changing, when it is changing, what users must do, and where they can get help. Segment messages for executives, managers, frontline workers, remote users, and IT support staff. Provide short training for Outlook, Teams, OneDrive sync, SharePoint collaboration, MFA registration, mobile access, and any new security prompts. During cutover, publish support channels, known issues, and escalation paths. After migration, collect feedback and update training based on the real questions users ask.

Validate and Optimize After Cutover

Post-migration validation should confirm mailbox access, mail flow, calendar delegation, shared mailboxes, Teams access, SharePoint and OneDrive permissions, file integrity, mobile access, Conditional Access behavior, device compliance, and application integrations. Monitor Microsoft 365 service health, message trace, Entra sign-in logs, audit logs, help desk ticket trends, endpoint compliance, storage growth, license utilization, and adoption indicators. Remove temporary migration accounts, retire unused connectors, archive old systems only after business validation, and schedule a post-project security and licensing review.

Key takeaways

• Treat Microsoft 365 migration as a modernization project covering identity, security, compliance, licensing, endpoints, workloads, and adoption.
• Use Microsoft Entra ID, MFA, Conditional Access, cross-tenant access settings, and least-privilege administration as part of the migration foundation.
• Plan Microsoft Purview controls before moving sensitive data, including sensitivity labels, retention, DLP, audit, eDiscovery, and lifecycle governance.
• Review CSP and New Commerce Experience licensing before purchase or renewal, including monthly versus annual terms, add-ons, Teams licensing considerations, and post-migration reclamation.
• Tenant-to-tenant migrations need special planning for domains, identity matching, coexistence, Exchange, OneDrive, SharePoint, Teams, Power Platform, applications, and tooling.
• Microsoft Intune, Windows Autopilot, compliance policies, app protection policies, and endpoint security baselines help users become productive securely after migration.
• Copilot readiness depends on permissions cleanup, data classification, SharePoint governance, and secure content practices, not only license assignment.

If you are planning a Microsoft 365 migration, tenant consolidation, Intune rollout, licensing review, or Copilot readiness project, IT Partner can help assess your current environment and design a practical migration plan with minimal business disruption.