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Can the same email domain be used in two Office 365 tenants?

Hello,
for carve out reason we need to migrate 300 users about, from O365 Tenant (Source) to O365 Tenant (Target).
The first question is, can I share between the two Tenant the same e-mail domain during the coexistence phase?
To explain better, the goal is that during the migration time all users (migrated or not migrated) are able to send messages with the same e-mail domain, the original one.
Thanks in advance for your answer.
Regards
Cesare

  • Hello Cesare,

    Thank you for posting in the On Demand Migration for Email (ODME) forum. Typically, Microsoft does not allow the same SMTP domain to exist in two separate Office 365 tenants simultaneously. However, you may want to confirm this limitation with Microsoft directly.

    Generally speaking, most ODME customers migrating to a new Office 365 tenant leave the primary SMTP domain in the source tenant and set the target email address in the ODME user list to "user@targettenant.onmicrosoft.com". Then, as part of the migration process, you can set the source tenant to forward user mail to the new "user@targettenant.onmicrosoft.com" with ODME. Once the migration project is complete, and mail forwarding is in place, then you can move the primary SMTP domain to the new target tenant.

    Note: Moving the primary SMTP domain from the old tenant to the new tenant should not be performed in the middle of a migration. ODME tracks license usage based off of the source SMTP address, so if the source email address changes mid-migration, then each user will then consume an additional license.

    Another option would be to use the .onmicrosoft.com address for both the source and target mailbox addresses in the ODME migration user list. This option may provide the most flexibility, as you can move your primary SMTP to the target tenant at any time without affecting your ODME licenses.

    Example:

    Source Mailbox Target Mailbox

    user@sourcetenant.onmicrosoft.com user@targettenant.onmicrosoft.com


    Please let me know if you have any additional questions or need any additional clarification.

    Thanks,