Tenant-to-tenant migrations happen during mergers, acquisitions, divestitures, and rebranding. They're among the most complex M365 operations. Here's what you need to know.
When T2T Migration Happens
- Mergers & Acquisitions: Consolidating two companies into one tenant
- Divestitures: Splitting a division into its own tenant
- Rebranding: Moving to a new primary domain
- Regulatory: Separating data for compliance (EU data residency, etc.)
What Needs to Move
| Data Type | Complexity | Tool Options |
|---|---|---|
| Email & Calendar | Medium | Native (Cross-tenant) or BitTitan |
| OneDrive | Medium | ShareGate, BitTitan, Mover |
| SharePoint Sites | High | ShareGate, Quest |
| Teams | Very High | Manual + third-party |
| Azure AD Users | Medium | Azure AD Connect + PowerShell |
| Conditional Access Policies | Manual | Export/Import via Graph API |
| Intune Policies | Manual | Export/Import |
| DLP Policies | Manual | PowerShell export/import |
Step-by-Step Process
Phase 1: Discovery (Week 1-2)
# Count mailboxes and sizes
Get-Mailbox -ResultSize Unlimited |
Select DisplayName, PrimarySmtpAddress,
@{N='SizeGB';E={(Get-MailboxStatistics $_.Identity).TotalItemSize.Value.ToGB()}} |
Export-CSV mailbox-inventory.csv
# Count OneDrive usage
Get-SPOSite -IncludePersonalSite $true -Limit All |
Where-Object { $_.Url -like '*-my.sharepoint.com/personal/*' } |
Select Owner, StorageUsageCurrent |
Export-CSV onedrive-inventory.csv
Phase 2: Preparation (Week 2-4)
- Create target tenant and configure domains
- Set up Azure AD in target tenant
- Purchase licenses — use M365 license comparison to pick the right plans
- Configure cross-tenant trust (if using native migration)
- Set up migration tool (BitTitan, ShareGate, or native)
Phase 3: Migration (Week 4-8)
Email Migration Order
- Shared mailboxes first (low risk, good test)
- Conference rooms and resources
- VIP/executive mailboxes (during low-traffic hours)
- Regular users in batches of 50-100
DNS Cutover Sequence
Day 0: Lower TTL to 300 seconds
Day 2: Switch MX records to target tenant
Day 2: Update SPF, DKIM, DMARC
Day 2: Update Autodiscover CNAME
Day 3: Verify all mail flow
Day 30: Raise TTL back to normal
Phase 4: Validation (Week 8-10)
- Test email send/receive (internal and external)
- Verify calendar data and recurring meetings
- Check OneDrive file access and sharing
- Validate Teams channels and chat history
- Confirm mobile devices reconnected
- Run compliance checks
Cost Estimates
| Org Size | DIY Cost | With Migration Partner |
|---|---|---|
| 50 users | $500-1,000 (tools) | $2,000-5,000 |
| 200 users | $2,000-5,000 (tools) | $8,000-15,000 |
| 1000 users | $10,000-20,000 (tools + time) | $25,000-50,000 |
| 5000+ users | $50,000+ (tools + dedicated team) | Custom quote |
The "DIY cost" doesn't include internal labor, which is typically 2-5x the tool cost.
Biggest Risks
1. Teams Data Loss
Teams migration is the hardest part. Chat history, files, and channel configurations don't migrate cleanly with most tools. Plan for some data loss or extended parallel operation.
2. Shared Mailbox Permissions
Delegated permissions (Send As, Send on Behalf, Full Access) must be manually recreated in the target tenant.
3. Conditional Access Policies
These don't migrate. Document everything in the source tenant and recreate in the target.
4. Third-Party App Integrations
Every app using OAuth tokens from the source tenant needs to be reconfigured. This includes:
- CRM systems (Salesforce, HubSpot)
- Ticketing systems (Zendesk, ServiceNow)
- HR platforms
- Custom line-of-business apps
When to Get Help
Tenant-to-tenant migrations are not a good DIY project for most organizations. The complexity, risk of data loss, and business disruption make professional help worth the investment.
Medha Cloud's tenant-to-tenant migration service handles the entire process with zero-downtime guarantees and dedicated project management. They've completed complex T2T migrations for organizations up to 50,000 users.
For a broader view of all migration options, see their M365 migration services overview.
Planning a tenant-to-tenant migration? Get a free migration assessment from Medha Cloud's certified Microsoft engineers.
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