You can use the remote move migration wizard on the Office 365 tab in the EAC on an Exchange server to move existing user mailboxes in the on-premises organization to the Exchange Online organization. Follow these steps:

1. Open the EAC, and then navigate to Office 365 > Recipients > Migration.

2. Click Add , and then select Migrate to Exchange Online.

3. On the Select a migration type page, select Remote move migration and then click Next.

4. On the Select the users page, click Add  and select the on-premises users to move to Office 365 and click Add and then click OK. Click Next.

5. On the Enter the Windows user account credential page, enter the on-premises administrator account name in the On-premises administrator name text field and enter the associated password for this account in the On-premises administrator password text field. For example, “corp\administrator” and a password. Click Next.

   Note:
   If you’ve already created a migration endpoint, you’ll receive an endpoint confirmation prompt for this step. If you’ve created two or more migration endpoints, you must choose an endpoint from the migration endpoint drop-down menu.

6. On the Confirm the migration endpoint page, verify that the FDQN of your on-premises Client Access server is listed when the wizard confirms the migration endpoint. For example, “mail.contoso.com”. Click Next.

   Note:

   The MRSProxy service on the Exchange Client Access servers automatically throttles the mailbox move requests when you select multiple mailboxes to move to Exchange Online. The total time to complete the mailbox move depends on the total number of mailboxes selected, the size of the mailboxes, and the configuration of the MRSProxy. To learn more about customizing the MRSProxy, see Message throttling.

7. On the Move configuration page, enter a name for the migration batch in the New migration batch name text field. Use the down arrow  to select the Target delivery domain for the mailboxes that are migrating to Office 365. In most hybrid deployments, this is the primary SMTP domain used for both on-premises and Exchange Online organization mailboxes. For example, contoso.com. Verify that the Move primary mailbox along with archive mailbox option is selected, and then click Next.

8. On the Start the batch page, select at least one recipient to receive the batch complete report. Verify that the Automatically start the batch option is selected, and then select the Automatically complete the migration batch check box. Click New.

You can use the remote move migration wizard on the Office 365 tab in the EAC on an Exchange server to move existing user mailboxes in the on-premises organization to the Exchange Online organization:

1. Open the EAC and navigate to Office 365 > Recipients > migration.

2. Click Add , and then select Migrate from Exchange Online.

3. On the Select the users page, select Select the users that you want to move and then click Next.

4. On the Select the users page, click Add  and then select the Exchange Online users to move to the on-premises organization, click Add and then click OK. Click Next.

5. On the Confirm the migration endpoint page, verify that the FDQN of your on-premises Client Access server is listed when the wizard confirms the migration endpoint. For example, “mail.contoso.com”. Click Next.

   Note:
   The MRSProxy service on the Client Access servers automatically throttles the mailbox move requests when you select multiple mailboxes to move to Exchange Online. The total time to complete the mailbox move depends on the total number of mailboxes selected, the size of the mailboxes, and the properties of the MRSProxy. To learn more about customizing the MRSProxy, see Message throttling.

6. On the Move configuration page, enter a name for the migration batch in the New migration batch name text field. Use the down arrow to select the Target delivery domain for the mailboxes that are migrating to Office 365. In most hybrid deployments, this is the primary SMTP domain used for both on-premises and Exchange Online organization mailboxes. For example, contoso.com.

7. Choose whether to also move the archive mailbox for the selected user and enter the database name you’d like to move this mailbox to in the Target database text field. For example, Mailbox Database 123456789. Click Next.

8. On the Start the batch page, select at least one recipient to receive the batch complete report. Verify that Automatically start the batch is selected, and then select the Automatically complete the migration batch check box. Click New.