Move user's mailbox from one domain to another under same tenant..

Question

Hi, we had a merger with another firm, and as per the management some of our users (existing company) will move to the new company (new company).

Our existing company has on-premises AD & Exchange on cloud (Microsoft 365 Business Premium) services.

we have added this new company domain under the same tenant.

We have got a new AD server for the "NewCompany" (I want to keep this AD separate with Trust relationship between the two AD domains for sharing resources)

My concerns are how to move the users from existing company to new company with their mailbox's? if i delete the user from existing AD and create the same user with same details in new AD, will it get connected to the same mailbox? or do i need to export the whole mailbox to a pst and import it again in the new AD?

Thanks, in advance.

Rakesh P

Answer 1

Hi

to add to what @Jame Xu-MSFT has said in his answer - if the users are going to exist in the same tenant, then there is no need for migration. You should just need to change the SMTP addresses for the users to the new address.

The additional query from me is around Azure AD Connect. Lets say in your original company (Company A), you were using Azure AD Connect to sync identities and therefore had the UPNs for Company A defined for each user.

You've also mentioned that you have a S2S VPN in place to Company B, and have also added their domain to your existing O365 tenant.You haven't stated how you will be adding their users accounts to your O365 tenant - will you be adding these as Cloud-only or syncing them through your Azure AD Connect.

If its through Azure AD Connect, this is where things can get tricky as Company B may also have their UPNs defined on their AD for their users. So if you wanted to change the UPN for the Company A users, you would be attempting to sync the same UPN from 2 different AD's to a single tenant which may not work.

In short, for the users that need to change email address, you may need to convert them to cloud-only and change their primary SMTP to match the Company B UPN.

Hope this helps,

Thanks

Michael Durkan

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Answer 2

Hi @Rakesh P D'souza ,

Generally, to export the data in the mailbox into a PST file is the easiest way.

Or, there's no need for "migration". All you need to do is change the Primary SMTP address to point to the new domain, as well as any other attributes that make sense for your scenario (UPN for example).

You could refer to: Migrate mailbox to another domain same Tenant

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