If you plan to migrate or move mailboxes from on-premises Exchange Server to Office 365 or Microsoft 365, you may choose any of the four given methods to migrate mailboxes from on-premises Exchange Server to Office 365 or Microsoft 365.
- Cutover Migration for Exchange 2003 and later versions.
- Staged Migration for Exchange Server 2003 and 2007.
- Hybrid Migration for Exchange 2010 and later versions.
- IMAP Migration for Gmail, Exchange, Outlook.com, and other IMAP-enabled email servers.
In this article, we will discuss the IMAP migration method in detail and learn how to use this method for moving mailboxes from Exchange or other IMAP servers to Office 365 or Microsoft 365.
What is IMAP Mailbox Migration?
IMAP migration is a method to move mailboxes or content of user mailboxes from non-Exchange servers or IMAP-enabled servers to Office 365 or Microsoft 365. However, you may also use the method to move mailboxes from Exchange Servers with IMAP4 configuration.
How does IMAP Migration Work?
In IMAP migration, administrators are required to create user mailboxes on Office 365 or Microsoft 365 and assign licenses to activate the mailboxes. Then they need to create a CSV file containing the details of all email accounts or mailboxes that need to be migrated. The information contained in the CSV file varies based on the IMAP email server. However, it usually includes the mailbox or account user name, email ID, and password separated by commas.
The administrator must also create an endpoint to allow communication between the IMAP server and Office 365 to complete the migration. After creating the endpoint, the administrator must upload the CSV file on Office 365 tenant. Office 365 uses the information provided in the CSV file to establish connectivity and automatically sync the mailboxes from the source email server to the destination.
Once the migration is finished, the administrator must delete the IMAP migration batch to stop the synchronization and redirect the email messages to the new Office 365 server by updating MX records.
Things to Consider Before Using IMAP for Mailbox Migration
While IMAP migration may appear convenient, it has some limitations that you must consider while choosing the method for moving your mailboxes to Office 365.
- The IMAP migration only moves the emails along with attachments to Office 365. Other mail items, such as Contacts, Calendar items, Notes, Tasks, etc., are not migrated to Office 365 or Microsoft 365.
- You can move user mailboxes containing no more than 500,000 items. Also, the emails are migrated in descending order, i.e., newest to oldest.
- Emails larger than 35 MB are not moved during IMAP migration.
Impact on Email Services and Users
There’s no impact on the users’ access to their email accounts or email services by default. However, if you reset the email accounts passwords to create the CSV file for moving the mailboxes and the users don’t have the new password, they may fail to access their email accounts during or after the mailbox migration. You must share the new password with the respective user.
How to Use IMAP Migration for Moving Mailboxes?
To move mailboxes from on-premises or any IMAP-based email server, you must create user accounts and assign licenses to activate the mailboxes. You can use the Office 365 or Microsoft 365 Admin Center or PowerShell cmdlets to assign the licenses. You may assign Office 365 licenses individually or in bulk based on your requirements.
Next, you need to create a CSV file containing the email address, username, and password. You may use Notepad or Microsoft Excel/Google Sheets to create a CSV file.
Make sure there are no extra spaces.
Save the file as .csv and open Office 365 Exchange Admin Center.
Click Migration and then click Add migration batch.
Type the migration batch name. You can name it anything and choose Migration to Exchange Online. Click Next.
Select IMAP Migration from the Select the migration type: dropdown and click Next > Next.
Select Create a new migration endpoint and click Next.
Enter the Migration endpoint name, Maximum concurrent migrations, and Maximum concurrent incremental syncs. Click Next.
Enter the IMAP server address, choose encryption, and enter the port number. Click Next.
The endpoint will be saved. Click Next.
Click Download a CSV file with headers and sample user information. This will download the sample CSV file where you can enter the user information.
After entering the details, save the file and click Browse to select the CSV file. Click Next.
You may add filters to include or exclude mail folders or items during the migration. Click Next.
Select the user who will be notified once the migration is complete and select the desired option to start the migration automatically or manually. You may also schedule it.
Click Save. You will get the status after a while. Click Done.
You may further check the sync status in the migration batches.
Once the migration is completed, select the migration batch and click Delete to remove the batch.
At this stage, you have successfully moved your mailboxes from Exchange or any IMAP-enabled email server to Office 365 or Microsoft 365.
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To Wrap Up
When moving mailboxes from the Exchange Server, Staged or Cutover Migration is recommended. IMAP migration is not recommended for moving mailboxes from Exchange Server unless you are experiencing issues with the Cutover or Staged Migration.
You can also use an EDB converter software, such as Stellar Converter for EDB, to overcome the limitations and manual efforts required in IMAP, Staged, and Cutover migration methods. Besides, the software works with all Exchange versions, including Exchange 2019, 2016, 2013, 2010, 2007, 2003, 2000, and 5.5.
You can use the software to export the mailboxes from your on-premises Exchange database file (offline) directly to Office 365 tenant. In addition, the software can export the mailboxes at up to 4x speed and automatically maps the source and destination mailboxes. This makes it easier and faster to move mailboxes between on-premises Exchange and Office 365.