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Mailboxes are on-premises, and you like to migrate a mailbox or bulk migrate mailboxes to Office 365. However, there are important steps involved before you start a migration. This article will show how to migrate mailboxes from Exchange on-premises to Exchange Online step by step.
Table of contents
- Create Exchange on-premises mailboxes CSV file
- Migrate mailboxes from on-premises to Office 365
Before you start to migrate mailboxes to Microsoft 365, it’s good to:
- Know the difference between New-MigrationBatch or New-MoveRequest in Exchange
- Install and configure Azure AD Connect
- Run the Hybrid Configuration Wizard
- Assign Office 365 licenses to the on-premises mailboxes
- Exchange Hybrid test plan checklist
- Export mailbox permissions to CSV file
- Export mailbox folder permissions to CSV file
- Disable EWS throttling in Office 365 – Exchange Online to speed up the migration*
*When there is a single mailbox or a couple of mailboxes to migrate, you don’t need to disable EWS throttling in Office 365.
Create Exchange on-premises mailboxes CSV file
Go through the steps below to create a CSV file with the on-premises Exchange mailboxes you want to migrate to Exchange Online.
Export Exchange on-premises mailboxes to CSV file
Sign in to Exchange Admin Center. Navigate to recipients > mailboxes. Click the more icon in the toolbar and click on Export data to a CSV file.
Check the checkbox EMAIL ADDRESS. Click Export.
It will download the CSV file to the Downloads folder by default. If a prompt shows up, make sure to save the CSV file.
In the next step, you will edit the CSV header.
Edit CSV header
It’s essential to edit the CSV file before uploading the CSV file in the next step. If you don’t do that, it will not work when uploading, and an error shows up.
Go to the file and rename ExportData.csv to MigrationBatch01.csv.
Place good attention and edit the CSV header. Remove the space between EMAIL ADDRESS.
It needs to look like EMAILADDRESS. Save the file.
Edit mailboxes in CSV file
Remove mailboxes in the CSV file that you do not want to migrate to Exchange Online.
Next, you will create a new migration batch and upload the CSV file.
Migrate mailboxes from on-premises to Office 365
Go through the below steps to migrate mailboxes from on-premises Exchange to Exchange Online in Office 365.
Create migration batch to move mailboxes
Sign in to Microsoft 365 Exchange Admin Center. Navigate to Migration > Add migration batch.
Give the new migration batch a name. In our example, MigrationBatch01. Select the mailbox migration path Migration to Exchange Online. Click Next.
Select the migration type Remote move migration. Click Next.
Select migration endpoint Hybrid Migration Endpoint – EWS (Default Web Site).
Note: The Hybrid Configuration Wizard did set up the migration endpoint.
You can select the Manually add users to migrate. Search and add the users to migrate to Office 365.
The option to manually add users to migrate is excellent if you have a:
- Single Exchange on-premises mailbox to migrate to Office 365
- Couple of Exchange on-premises mailboxes to migrate to Office 365
If you have a lot of mailboxes to migrate to Office 365, you want to select the CSV file option.
Select Migrate from CSV file. Browse to the CSV file that you exported in the earlier step. Click Next.
Select the Target delivery domain. Click Next.
In the Schedule batch migration step:
- Add the mailbox that needs to receive the batch complete report
- Select Automatically start the batch
- Select Manually completing the batch later
- Click Save.
Note: Selecting the Manually completing the batch later will sync the mailboxes up to 95%. After that, every 24 hours, a delta sync will occur. You then can decide when to complete the mailboxes. That is an excellent way to complete the migration batch in the evening or the weekend.
Read more: Schedule mailbox batch migration »
Batch creation is successful. Click Done.
Check mailbox move progress
Select MigrationBatch01 in the list view.
Click in the details pane on View details to get more information regarding the mailboxes move.
It first will start with Validating the mailboxes move request. After that, the status will change to Syncing or Failed. You can always click the Refresh button.
Give it time to show the mailbox data consistency score, how many mailbox items synced, and items skipped.
Click on a mailbox that finished syncing.
Click on the failed mailbox to check why the status failed shows up.
In this example, it shows:
Error: MigrationPermanentException: You can’t use the domain because it’s not an accepted domain for your organization.
Another error that you can get is: Target mailbox doesn’t have an SMTP proxy matching.
After fixing the failed mailbox, Refresh and verify that all the mailboxes are in sync with Microsoft 365/Office 365. Everything looks great to complete the migration batch.
Note: The Microsoft 365 Exchange Admin Center status is delayed when retrieving the mailbox status compared with PowerShell. We recommend to Get mailbox migration status with PowerShell.
In the next step, you will complete the mailboxes in the migration batch.
Keep reading: Check which mailboxes are in sync with Office 365 »
Complete mailbox migration batch
Click the migration batch in the list view. Click on Complete migration batch to start the completing mailboxes process.
Note: You can’t complete an individual mailbox from the Microsoft 365 Exchange Admin Center, but it’s possible to do that with PowerShell. Read more: Complete individual mailbox move request from migration batch.
The mailbox migration status will change to Completing.
In the next step, which is the last step, you will verify the migration batch completion status.
Verify migration batch completion
Migration batch Completed without errors. You can see if all the mailboxes are finalized or failed in the details pane on the right side. In our example, eleven mailboxes failed because they already are hosted in the target database. If you have other errors, troubleshoot further.
The on-premises mailboxes are now successfully migrated to Office 365. Also, the migration report is sent to the mailbox you set up in the previous step.
Keep on reading: Complete migration batch with PowerShell »
You learned how to migrate Exchange on-premises mailboxes to Office 365. First, export the mailboxes to CSV file from on-premises Exchange Admin Center. Then, remove the email addresses you don’t want to move from the CSV file.
Don’t forget to edit the header and save the CSV file. If you don’t, an error appears when uploading the CSV file. Create a new migration batch in Microsoft 365 Exchange Admin Center and upload the CSV file. Keep an eye on the migration progress status.
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