I need help with migration

Question

Hello

I need to migrate our account to a wider business due to a merger.

In general, I need to change the domain name while keeping my email history without losing any data.

On top, I need to ensure after that after the change the extensions of our emails from (i.e @ abc.com to @ abd.com) to have access to the emails which are still being sent to @ abc.com, for example being automatically forwarded to the new email addresses.

Answer 1

Hello IBN

Thank you for your inquiry and welcome to Microsoft Q&A forum.

Regarding your requirement to change your email domain from @abc.com to @abd.com while preserving all mailbox history and ensuring mail sent to the old domain continues to be delivered. you can proceed to add and change domain for user in admin center while keep the old domain active in the tenant and set as alias for users. You can follow the steps below:

1. Add and Verify New Domain
   • Add abd.com in Microsoft 365 Admin Center.
   • Complete DNS verification and configure SPF/DKIM/DMARC for the new domain.
2. Update User Sign‑In and Email Addresses
   • Change each user’s User Principal Name (UPN) to ******@abd.com for sign‑in.
   • Set ******@abd.com as the primary SMTP address and keep ******@abc.com as an alias.
   • This ensures:
   • Users sign in with the new domain.
   • All historical emails remain intact.
   • Emails sent to @abc.com continue to deliver automatically—no forwarding rules required.
3. Set abd.com as Default Domain
   • Make abd.com the default for new accounts.
4. Testing & Validation
   • Verify mail flow for both domains.
   • Confirm Outlook/OWA sign‑in and Autodiscover.
   • Validate shared mailboxes, distribution lists, and apps that send mail.
5. Communication & Cutover
   • Notify users and partners of the upcoming change.
   • Schedule the UPN and primary SMTP update during a low‑impact window.

By retaining abc.com as an alias, you avoid mail loss and there no need for complex forwarding. Users will send as @abd.com, but any mail sent to @abc.com will still arrive in their mailbox.

I hope this answer able to clarify your concern. If you have any additional question, feel free to comment below. I be more than happy to assist.  

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