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Office 365 staged migration
As part of a Microsoft 365 or Office 365 deployment, you can migrate the contents of user mailboxes from a source email system to Microsoft 365 or Office 365 through O365 Migration Services. When you do this over time, it's called a staged migration. A staged migration is recommended when: Your source email system is Microsoft Exchange Server 2003 or Microsoft Exchange Server 2007. You have more than 2,000 mailboxes. How does staged migration work? The main steps you perform for a staged migration, and the results for your users, are shown in the following illustration. Here's a description of the staged migration shown in the illustration. The administrator synchronizes the list of users between their on-premises environment and Microsoft 365 or Office 365. See how-to steps in Prepare for a staged migration. The administrator creates a comma-separated value (CSV) file that contains a row for each user whose on-premises mailbox will be migrated in the migration batch. See how-to steps in Create a list of mailboxes to migrate. The administrator creates and runs a staged migration batch by using the migration dashboard in the Exchange admin center. See how-to steps in Connect Office 365 to your email system, Migrate your mailboxes, and Start the staged migration batch. After the administrator starts the migration batch, Exchange Online does the following: Verifies that directory synchronization is enabled. Checks that a mail-enabled user exists in the Microsoft 365 or Office 365 organization for each user listed in the CSV file. Mail-enabled users are created in Microsoft 365 or Office 365 as a result of the directory synchronization process. Converts the Microsoft 365 or Office 365 mail-enabled user to an Exchange Online mailbox for each user in the migration batch. Begins initial synchronization. Exchange Online processes up to N migration requests at one time. N represents the maximum number of concurrent migrations that the administrator specified when creating the migration endpoint used for the migration batch. By default, initial synchronization is performed on 20 mailboxes at a time until all mailboxes in the migration batch are migrated. Configures mail forwarding. The TargetAddress property on the on-premises mailbox is configured with the email address of the Exchange Online mailbox. This process means that mail sent to the on-premises mailbox is forwarded to the corresponding Exchange Online mailbox. After it creates the Exchange Online mailbox and configures mail forwarding for each user in the CSV file, Exchange Online sends a status email message to the administrator. This status message lists the number of mailboxes that were successfully migrated and how many couldn't be migrated. The message also includes links to migration statistics and error reports that contain more detailed information. At this point, users can start using their Exchange Online mailboxes. As part of initial synchronization, Exchange Online then migrates all email messages, contacts, and calendar items from the on-premises mailboxes to Exchange Online mailboxes. Exchange Online sends a final migration report when the data migration is complete. After a migration batch is complete and the administrator verifies that all mailboxes in the batch are successfully migrated, the administrator can convert the on-premises mailboxes to mail-enabled users. See how-to steps in Convert on-premises mailboxes to mail-enabled users so that migrated users can get to their email. If a user opens their mailbox with Outlook, the Autodiscover service tries to connect to the on-premises mailbox. After you convert on-premises mailboxes to mail-enabled users, the Autodiscover service uses the mail-enabled user to connect Outlook to the Exchange Online mailbox after the user creates a new Outlook profile. The administrator creates additional migration batches, submitting a CSV file for each one. The administrator runs additional migration batches. The administrator resolves any issues. After all on-premises mailboxes in a batch are successfully migrated, the administrator deletes the migration batch. See how-to steps to Delete the staged migration batch. Users can use their Exchange Online mailboxes. The administrator, to complete the transition to Exchange Online and Microsoft 365 or Office 365, performs post-configuration tasks such as: Assign licenses to Microsoft 365 or Office 365 users. Configure the MX record to point to your Microsoft 365 or Office 365 organization so that email is delivered directly to Exchange Online mailboxes. Create an Autodiscover Domain Name System (DNS) record for your Microsoft 365 or Office 365 organization. Hope you find this helpful. To learn more about Cutover Migration or to Migrate From Slack to Teams, visit O365CloudExperts.
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