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Summary: Businesses explore transitioning from On-premises Exchange to Office 365 due to efficient cloud platforms. Several methods, including CSV file use, cutover migration, and hybrid migration, simplify the process. The Kernel Office 365 Migration tool ensures a seamless transition with minimal preparation.

With the emergence of highly effective cloud platforms and their streamlined services, numerous business proprietors are exploring the transition from On-premises Exchange to Office 365. Exchange mailbox sizes are typically substantial, making the process of migrating them a potentially time-consuming and error-prone endeavor. Fortunately, there are several methods available to assist you in accomplishing your migration objectives.

Method 1- Use CSV file

A CSV file is an ideal choice for efficiently migrating large mailboxes to Office 365 in bulk. You can employ a CSV file in conjunction with either the Exchange admin center (EAC) or the New-MigrationBatch cmdlet in Exchange Management Shell to establish a migration batch. The following migration scenarios benefit from the use of a CSV file:

  • Onboarding remote move migration

    The onboarding remote move migration method facilitates the migration of mailboxes from on-premises Exchange to Office 365, particularly in the context of an Exchange hybrid deployment scenario.

  • Offboarding remote move migration

    Offboarding remote move migration serves as the inverse of onboarding remote move migration. In this process, you can migrate Office 365 mailboxes back to your on-premises Exchange environment.

  • Staged Exchange migration

    In Staged Exchange migration, you can migrate a subset of mailboxes from an on-premise Exchange organization to Office 365.

  • IMAP migration

    In this type of migration, you can migrate mailbox data from an IMAP server (including Exchange server) to Office 365.

How to use CSV file for bulk mailbox migration?

The CSV file follows a specific format in which you can input the necessary mailbox information. The first row, known as the header row, contains the names of attributes or fields, arranged vertically. Each attribute is separated by a comma. Each subsequent row below the header row represents a user and provides all the required information for the migration. The attributes in each row should be in the same order as the attribute names in the header row.

It is advisable to create the CSV file using a text editor or, even better, in a Microsoft Excel Spreadsheet, which provides dedicated cells for each attribute and makes it easier to organize the information. Always remember to save the file in either .csv or .txt format.

Note: If a record has a null attribute value, you should leave that attribute blank but include a comma to separate it from the next attribute in the CSV file.

The following section will describe you what attributes you should enter for different methods of migration –

  • Staged Exchange Migration

    Attribute – EmailAddress, Password, ForceChangePassword.

  • IMAP migrations

    Attribute – EmailAddress, UserName, Password.

Method 2- Cutover migration

Cutover migration is a suitable approach when the number of mailboxes in the Exchange account is less than 2000. Here’s a brief overview of the cutover migration process conducted by an Exchange Administrator:

  1. Exchange Administrator briefs all users about upcoming changes and verifies the domain ownership.
  2. Create empty mail-enabled security groups in Office 365.
  3. Connect Office 365 to the on-premises email system.
  4. Migrate the mailbox and verifies the process.
  5. Grant access rights to the users.
  6. Configure the domain to begin routing email to Office 365 directly.
  7. Verify the routing has changed, and then delete the cutover migration batch.
  8. Complete post-migration tasks in Office 365 like creating and assigning a new license to the user), domain name system (DNS).
  9. Send a welcome letter to all the users and provide complete information that how they can log in to their accounts.
Method 3- Hybrid migration

The Hybrid Migration is done when you have to maintain both on-premises exchange and online Exchange. This can be done when:

  • You are using either Exchange 2010 or 2013
  • You want to migrate in small batches
Quick & Precise Migration

The Kernel Office 365 Migration tool is a powerful solution designed to migrate an unlimited number of mailboxes from both on-premise and hosted Exchange environments to Office 365. This tool eliminates the need for extensive prior preparation and ensures a comprehensive migration of mailboxes. Furthermore, it provides a detailed report upon successful completion of the migration. Let’s explore how this migration tool operates:

  1. This is the home screen of the migration tool. Here in the Add Source section click on the Add button to add the Exchange account.
    Office 365 Migration tool
    Note: When dealing with multiple mailboxes for migration, you can streamline the process by adding both source and destination mailboxes using a CSV file. The tool typically offers a sample CSV file for download. Once you’ve filled in the necessary details according to your migration requirements, you can import the CSV file into the tool.
  2. Now, in the Office 365/Exchange Login dialogue box, enter the Exchange credentials in the designated boxes. Now, check the box “List all Mailboxes using above credentials (Use Global Administrator login details)” and click on the Add button.
    List all Mailboxes using above credentials
    Note: This demonstration is for bulk migration, that’s why we are adding multiple mailboxes, if you want to add a single mailbox, then after adding the credentials, click on the Add button.
    bulk migration
  3. Once the mailboxes are added, click on the Add button under the Add Destination section.
    Add Destination
  4. Here, add the Office 365 credentials correctly, check the box to add multiple mailbox just as earlier and click the Add button.
    add the Office 365 credentials
  5. In the next step, map the source and destination accounts and click on Set Filter and Migrate button.
    map the source and destination accounts
  6. In the next step, select where you want to migrate the mailboxes. Select one option from the drop-down and click on the Migrate button.
    Click on Migrate
  7. In the next step, apply filters to the migration process. By applying this, you can customize the whole process – you can apply filters like Date, Item type, Exclude deleted/empty folders, and many more. Click on I am OK, Start Migration.
    apply filters
  8. As the process starts, wait for it to finish and click on the OK button.
    process starts

Note: You can save the CSV report of the process by clicking on the Save report to CSV option.


While various native methods for mailbox migration to Office 365 can be technically complex, the Kernel Office 365 Migration tool eliminates the need to navigate through these intricacies. With this tool, you can commence your migration process without encountering such complexities. Simply begin by mapping your mailboxes and filtering their content.

Kernel Office 365 Migration