Domain Migration Between Office 365 Tenants
Plan and execute domain transfers between Office 365 tenants with minimal downtime using Cloudiway Mail Routing.
Overview
This guide outlines the complete process for transferring a domain between two Office 365 tenants while minimizing downtime on inbound mail using Cloudiway Mail Routing. The procedure requires advance coordination with Cloudiway Services.
Advance Planning Required
At least 5 business days' notice is necessary to arrange setup and testing before the scheduled cutover. Contact Cloudiway Services early in your planning process.
Prerequisites
Before You Begin
- Global Administrator access to both source and target tenants
- Access to DNS management for the domain(s) being migrated
- Cloudiway Mail Routing service activated (contact sales)
- All mailbox data migrated to the target tenant
- Users created in target tenant with appropriate licenses
Step-by-Step Process
Reduce TTL Values
Before initiating the switch, lower your MX record TTL to the minimum allowed value (typically 300 seconds or 5 minutes).
This ensures DNS changes propagate quickly during the migration.
Configure Mail Routing
Collaborate with Cloudiway Services to establish mail routing between source domain names and the technical target domain.
Example Configuration:
| Source Domain | Target Domain |
|---|---|
| company.com | target.onmicrosoft.com |
| company2.com | target.onmicrosoft.com |
Update MX Records to Cloudiway
Modify your MX records to point to the Cloudiway mail routing IP. Cloudiway Services will provide the specific IP address during setup.
Execute Final Delta Pass
Run a final delta synchronization to transfer any remaining data that was created or modified since the initial migration.
Verify Email Flow
At this stage, new messages arrive at the target tenant and all legacy emails are migrated. Verify that mail is flowing correctly before proceeding.
Safe to Proceed
The environment is now secure for domain detachment from the source tenant.
Remove Domain from Objects
Execute the domain removal script to remove the domain from all users, groups, and other objects in the source tenant.
# PowerShell - Remove domain from all users
Get-MsolUser -DomainName "company.com" | `
Set-MsolUserPrincipalName -NewUserPrincipalName `
{$_.UserPrincipalName -replace "company.com","source.onmicrosoft.com"} Domain Tenant Transfer
- Remove the domain from the source tenant (Microsoft 365 Admin Center → Settings → Domains)
- Add the domain to the target tenant
Verify Domain Ownership
- Add a TXT DNS record as provided by Microsoft for domain verification
- Complete the domain ownership verification process in the target tenant
Reassign Domains to Users
Update SMTP addresses and UPN values in the target Active Directory, then synchronize changes to Microsoft 365.
Update MX Records to Target
Redirect MX records to point directly to the target Office 365 infrastructure, bypassing Cloudiway mail routing.
Migration Complete
The domain migration process is finalized. Users can now access their mailboxes using the migrated domain on the target tenant.
Verification Checklist
- Domain appears in target tenant admin center
- Users can sign in with domain email addresses
- Inbound mail delivers correctly to target mailboxes
- Outbound mail sends with correct domain addresses
- Calendar invites work correctly
- MX records point to target Office 365