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Migrating exchange 2019 to office 365 with a new domain controller

Pedro Jose Martinez 40 Reputation points
2023-06-22T11:56:34.3566667+00:00 

Currently we have an AD in windows server 2016 and an exchange server 2019 connected. We want to migrate to office 365 and update the Ad to a windows server 2022 keeping the same domain and the migration process has to be done gradually.
The MX records will point to the exchange until the end of the migration and when finished they will be changed to Office
If I create a new ad in ws2022 and I connect it with azureadconect to office 365, will the already migrated users and the old ones be able to connect to their mailboxes even if one is from the same domain? Will it detect that one account is from office and another from exchange?
Greetings
Exchange | Exchange Server | Management
Windows for business | Windows Server | Devices and deployment | Set up, install, or upgrade
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  1. Luca Lionetti 3,231 Reputation points
    2023-06-22T12:09:36.5533333+00:00

    Hi,

    Welcome to Microsoft Q&A community forum!

    For migrations from an existing on-premises Exchange Server environment, an administrator can migrate all email, calendar, and contacts from user mailboxes to Microsoft 365 or Office 365.

    An administrator performs a staged or cutover migration to Microsoft 365 or Office 365. All email, contacts, and calendar information can be migrated for each mailbox.

    There are three types of email migrations that can be made from an Exchange Server:

    Migrate all mailboxes at once (cutover migration) or Express migration

    Use this type of migration if you're running Exchange 2003, Exchange 2007, Exchange 2010, or Exchange 2013, and if there are fewer than 2000 mailboxes. You can perform a cutover migration by starting from the EAC; for more information, see Perform a cutover migration to Microsoft 365 or Office 365. For information on how to use the Express migration, see Use express migration to migrate Exchange mailboxes to Microsoft 365 or Office 365.

    Important

    With cutover migration, you can move up to 2000 mailboxes, but due to length of time it takes to create and migrate 2000 users, it's more reasonable to migrate 150 users or less.

    Migrate mailboxes in batches (staged migration)

    Use this type of migration if you're running Exchange 2003 or Exchange 2007, and if there are more than 2000 mailboxes. For an overview of staged migration, see What you need to know about a staged email migration to Microsoft 365 or Office 365. To perform the migration tasks, see Perform a staged migration of Exchange Server 2003 and Exchange 2007 to Microsoft 365 or Office 365.

    Migrate using an integrated Exchange Server and Microsoft 365 or Office 365 environment (hybrid)

    Use this type of migration to maintain both on-premises and online mailboxes for your organization and to gradually migrate users and email to Microsoft 365 or Office 365. Use this type of migration if:

    You have Exchange 2010 and more than 150-2,000 mailboxes.

    You have Exchange 2010 and want to migrate mailboxes in small batches over time.

    You have Exchange 2013 or later.

    For more information, see Use the Microsoft 365 and Office 365 mail migration advisor.

    For Azure AD Connect you can use your 2016 domain controller to sync the users to azure AD, you don't need to upgrade to windows 2022. The Active Directory schema version and forest functional level must be Windows Server 2003 or later. The domain controllers can run any version as long as the schema version and forest-level requirements are met.

    The users synchronized to azure ad can use office 365

    this table can help you decide on the type of migration

    Fewer than 150Over a weekend or a few days.Cutover or Express migration.Fewer than 150Slowly, by migrating a few users at a time.Exchange HybridOver 150Over a weekend or a few days.Exchange HybridIf you have more than 150 mailboxes, the best method is to use an Exchange hybrid migration where you can migrate a limited number of users at a time. This is because cutover migration performance suffers when you try to migrate more than 150 mailboxes.Over 150Slowly, by migrating a few users at a time.Exchange Hybrid

    If you want to use only azure AD as authenitcation mechanism, you have the possibility to remove the old domain controller and use only azure AD. But this option depends on the on prem services.

    Hope this helps

    Cheers

    Luca

    Please "Accept as Answer" and Upvote if the answer provided is useful, so that you can help others in the community looking for remediation for similar issues

    1 person found this answer helpful.

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  1. Andy David - MVP 157.8K Reputation points MVP Volunteer Moderator
    2023-06-22T12:00:07.6333333+00:00

    Yes, that is it how it works. Once you move a mailbox to 365, the user will be able to access their mailbox in Exchange Online. Existing on-prem mailboxes will continue to work. Do no change the Autodiscover record to point to 365 until you have moved all mailboxes to 365

    https://learn.microsoft.com/en-us/exchange/decommission-on-premises-exchange

    1 person found this answer helpful.
  2. Pedro Jose Martinez 40 Reputation points
    2023-06-22T12:57:50.8266667+00:00 
    So I can use a hybrid migration taking the azuread users from an AD in ws2022 and connect the office to the exchange connected to another AD? of course they will have the same users and upns

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