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Professional Services

Microsoft 365 Tenant-to-Tenant Migration

How we executed a Microsoft 365 tenant-to-tenant migration for 500+ users — mailboxes, OneDrive, SharePoint, Teams and domain cutover with zero data loss.

Client:
Multinational professional-services group
Industry:
Professional Services
Published:
Microsoft 365 Tenant-to-Tenant Migration

At a glance

500+

Users migrated

15 TB

Business-critical data moved

0

Data loss

Overview

Following a corporate restructuring, a multinational professional-services group had to separate its Microsoft 365 environment from the parent company's tenant — mailboxes, OneDrive, SharePoint sites, Teams, distribution groups and the permissions that tie them together.

Mignet planned and ran the migration in departmental waves so the business kept working throughout, then cut the domain over on a scheduled window with a tested rollback path.

The challenge

  • More than 15 TB of business-critical data to move
  • User access and SharePoint permissions had to be preserved
  • Email continuity could not be interrupted
  • No disruption permitted during working hours
  • Secure transfer and compliance obligations
  • Multiple departments and locations to coordinate

Our approach

  1. 01

    Assessment & discovery

    • Mapped source tenant configuration and mailbox sizes
    • Inventoried SharePoint sites, permissions and Teams structure
    • Reviewed OneDrive usage and domain dependencies
    • Produced a detailed migration roadmap from the findings
  2. 02

    Migration planning

    • Department-based migration waves
    • End-user communication plan
    • Risk assessment with mitigation and rollback strategy
    • Cutover schedule plus validation and test procedures
  3. 03

    Tenant preparation

    • Provisioned user accounts and licensing in the destination tenant
    • Applied security and conditional-access policies
    • Configured Exchange Online, SharePoint and Teams
  4. 04

    Data migration

    • Exchange Online: user and shared mailboxes, calendars, contacts, distribution groups
    • OneDrive for Business: files, sharing permissions and ownership
    • SharePoint Online sites with permission mapping
    • Teams structure, channels and membership
  5. 05

    Domain cutover & post-migration support

    • Scheduled DNS and domain cutover with a tested rollback
    • Mail-flow and access validation immediately after cutover
    • Hypercare support for end users and administrators

Results delivered

  • All users, mailboxes and data migrated with no loss
  • Email continuity maintained throughout the cutover
  • Permissions and sharing preserved in SharePoint and OneDrive
  • Business operations continued without working-hour disruption
  • A clean, fully separated tenant ready for independent governance

Frequently asked questions

What is a tenant-to-tenant migration?

It moves users, email and data from one Microsoft 365 tenant into another — typically after an acquisition, divestment or restructuring.

How long does a tenant migration take?

It depends on user count and data volume; SMB environments typically complete in one to seven days, larger estates are phased over several weeks.

Is there downtime during migration?

Minimal, when the migration is phased and the domain cutover is scheduled outside business hours with validation checks on both sides.

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