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SysAd09-5307 asked KyleXu-MSFT edited

Migrating Existing Forest with Exchange 2019 to a new forest domain also using AD Connect for o365 syncing

I haven an existing forest/domain that have some issue and I want to create a brand new forest/domain and bring over users etc ADMT. I want to know what is the best way to accomplish this with the Exchange 2019 in mind. I wanted to minimize down time and have read several articles about cross migration to a new Exchange server, but will the domain controller portion have to be done first then the exchange? Any help is appreciated!

office-exchange-server-administrationwindows-active-directory
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@SysAd09-5307
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KyleXu-MSFT answered KyleXu-MSFT commented

@SysAd09-5307

There are exist two ways to migrate mailboxes:

Way 1:
1. Migrate all mailboxes to Exchange online, then decommission the old Exchange on-premises.
2. Create hybrid and AAD sync with new domain/forest, migrate mailboxes back to Exchange on-premises, if you want.

Way 2:

  1. Migrate all mailboxes to Exchange on-premises, then remove hybrid and AAD connect.

  2. Use ADMT to do a cross-forest migration to migrate mailbox from old domain to new domain. You could have a look about this article(Suitable for Exchange 2019) Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

  3. Create AAD sync and hybrid in new domain.

If there doesn't exist hybrid in your organization, I think the second method is more suitable.


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Hi There,

Thank you for your quick response. I want to clarify something. So I just want to create a new forest and domain on its own. I want to migrate the AD users to the new domain using ADMT. I use Exchange 2019 on premise, no cloud boxes and no plans. The Azure sync client is only used for teams so users can use Teams. So I read your article about using ADMT to move users to the new exchange server in the new domain. So my question is.. will that method kill two birds with one stone.. migrate the user (AD) and mail box and other AD related materials computer accounts OU etc? My original thought was to Migrate the domain to the new forest and then cross migrate the exchange mail boxes.. then reinstall the Azure sync client.

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Yes, the cross-forest migration is a way to migrate mailboxes and AD account from source domain to target domain.

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LimitlessTechnology-2700 avatar image
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LimitlessTechnology-2700 answered

Hi there,

You can Prepare mailboxes for cross-forest moves using the Exchange Management Shell. Exchange Server supports mailbox moves and migrations using the Exchange Management Shell New-MoveRequest and New-MigrationBatch cmdlets. You can also move the mailbox to the Exchange admin center (EAC).

https://docs.microsoft.com/en-us/exchange/architecture/mailbox-servers/prep-mailboxes-for-cross-forest-moves-in-powershell?view=exchserver-2019

Hope this answers all your queries, if not please do repost back.
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