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Cutover into existing “Live” Tenant

When migrating into an existing Microsoft 365 tenant that users already are “live” in (i.e. they send/receive mail from an account in the target with a different domain than their source account uses), considerations must be taken to ensure proper mail delivery takes place before the cutover is performed.

If the customer is performing the DNS Cutover, the below process should be followed.

Cutover process

Pre-Cutover actions to prepare for a migration into a target tenant where users are already live with a mailbox that includes a different domain than the source platform’s primary domain:

1. Customer – Provision user accounts with the domain.onmicrosoft.com temp domain that Microsoft provides.
2. Transend – Perform Stage-1 migration to target accounts with the temp domain.onmicrosoft.com domain set as the primary email address.
3. Transend – Confirm Stage-1 migration is complete.
4. Customer – Add primary domain from the source tenant to the target tenant (domain.com).
5. Customer – Just before MX records are updated (DNS Cutover), update target accounts to change their primary email address from the domain.onmicrosoft.com temp domain to the primary domain (domain.com).
6. Customer – Update DNS records.
7. Transend – Perform Stage 2 & 3 migrations.