Topic: How to implement Tenant to Tenant Office 365 migration?

Stages To Move Domain From One Office 365 Tenant To Another
Migrating the resources and information of one tenant that uses Office 365 to another involves various steps. A basic classification divides them into two, namely the Preparation (or Pre-migration stage) and the Migration process itself.



Preparation for Office 365 Tenant To Tenant Migration
Before commencing with the migration process, one has to go through a multi-step preparatory process. This will help prepare one for the migration process and complete it smoothly. The following steps are involved.

Step 1 – Domain Preparation
There should be sufficient space or room in the target tenant’s Office 365 to ensure the successful migration of all data from the source tenant. It could entail obtaining additional licenses, as well.
Secondly, both the source tenant and the target tenant will require the opening of administrator accounts. Also, specific migration tools might need the creation of additional admin accounts.
It is also necessary to create user mailboxes, resource mailboxes, and distribution groups in the target tenant.
At times, performing Active Directory Domain Services (AD DS) consolidation using AD DS tools might be necessary. The synchronization of the source and the target domain is the next step to follow.
The final step of the domain preparation stage is to train the end-users on how to use Office 365 post-migration.
Step 2 – Verification of the Domain
Commence the process of verifying the target tenant domain in Office 365.
The addition of a source domain in the admin center of the target Office 365 and the creation of TXT records in DNS have to be performed.
However, one should ensure that the domain is in use for only one target tenant lest the verification process should fail. It will now take around 72 hours for the change to take effect.

Step 3 – Scheduling the Migration
The first step involves generating a list of user mailboxes for migration and creating a CSV file for mapping.
Note down the lowest value of Time To Live (TTL) on the Mail Exchanger (MX) record of the primary email domain.
The next step is to disable the directory sync for the source tenant.
Step 4 – Facilitating the Migration
Change the primary MX record to an unreachable value to stop the flow of inbound mail to the source tenant. It becomes easy because of the noting down of the lowest value of TTL on the MX record.
Ensure erasure of all objects from the primary mail domain in the source tenant before the transfer of Office 365 mailbox to another account.
The final step is preparing the target domain by verifying the source tenant in the target domain. One should ensure to initiate this step one hour after performing the previous actions.
If one uses Active Directory Federation Services (AD FS), one has to configure a new domain in the target tenant for AD FS.
One should also activate new users in the target domain as well as assign new licenses.
The primary email address for the new users must be the source domain. Communicating the passwords to the new users is also necessary.

I hope this method will be helpful!
Mark Wilson