Introducing Microsoft 365! How to migrate email data? [Outlook]

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When introducing Microsoft 365 for the first time, you have to migrate mailboxes and data.

Microsoft 365 stores data in the cloud environment, so there will be work to move data that was previously stored in another email service or on-premises server to the cloud.

Data migration can be a big undertaking, but rest assured that it’s supported by a variety of migration tools.

This article explains the flow from the preparation stage to the actual work for those who are considering migrating to Microsoft 365.

It also introduces how to migrate from the current email environment, so please use it to prepare for the migration work.


When migrating to Microsoft 365, large-scale data migration and extensive system changes are required, so careful preparation is required.

Find out what your IT department and admins should do to prepare.

1. Data inventory

Scheduling a migration requires knowing exactly what data and scope to target.

Let’s start with data inventory.

At this time, if you try to bring all the data, the amount of work will be enormous.

It is a good idea to identify and organize unnecessary data on the occasion of cloud migration.

2. Scheduling

Once you know what data to migrate, create a schedule.

User work will also occur, so plan to avoid busy periods and other system change periods.

Also, data migration is time consuming and impossible to complete all at once.

Prioritize your data and establish an order of work.

3. Selection of migration tool

Choose a tool for your migration to Microsoft 365.

Once you have decided on a tool, you will be able to create a detailed work plan.

The types of tools are explained in the next chapter.

What is Microsoft 365 migration tool

When migrating to Microsoft 365, it is necessary to move a large amount of data, but there is a tool that can migrate data all at once, so you can rest assured.

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Migration tools include free tools and paid tools.

Understand the differences between each and choose the best tool for your purpose and budget.

Microsoft migration tool (free)

Microsoft provides migration tools such as “Migration Manager”.

These tools are available for free, so if you want to keep costs down, check out Microsoft’s migration tools to see if it’s possible.

If you use Microsoft’s free tools, you’ll need to do the work yourself, so you’ll need the resources and knowledge to do it.

Third-party migration tools and migration assistance services (paid)

Various Microsoft 365 migration services have been released by various companies.

Using paid third-party tools

  • Migrate emails, calendars, contacts and more all at once
  • Migrate from existing database to SharePoint

Advanced migration work such as is also possible.

In addition, there is migration support that consistently supports from identifying target data, schedule creation, migration work, and after-sales service.

If you want to perform migration work efficiently, you should consider using it.

Mailbox migration steps

Among the migration tasks to Microsoft 365, mailbox migration has a large impact on users, so it is necessary to pay particular attention to the work procedure and timing.

Let’s take a look at the overall workflow of a mailbox migration task performed by an administrator.

Here, we will introduce a method using Microsoft’s migration tool.

IMAP migration

The general flow when migrating from an IMAP format mailbox is as follows.

Migration from Gmail and Yahoo! Mail is also performed using this procedure.

  1. Create users in Microsoft 365
  2. Keep users informed of changes and impacts
  3. Obtain the source mailbox password or temporarily change the password to allow administrator access
  4. Create a list of source mailboxes as a CSV file
  5. Connect Microsoft 365 to your source email system
  6. Create Migration Endpoint in Exchange Admin Center
  7. Migrate mailboxes and optimize settings
  8. Register your domain with Microsoft 365
  9. Start routing Microsoft 365 emails
  10. stop syncing emails
  11. Guide users to start using

Cutover migration

This is the procedure for migrating on-premises email to Microsoft 365.

Exchange bulk migration allows you to migrate up to 2000 mailboxes to Microsoft 365, but due to heavy data, it is recommended to migrate no more than 150 mailboxes at once.

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Create a schedule, knowing that it will take a few days for your entire email structure to be migrated to Microsoft 365 and ready for use.

  1. Keep users informed of changes and impacts
  2. Prepare servers for bulk migration
  3. Create an empty security group in Microsoft 365
  4. Connect Microsoft 365 to your on-premises email system
  5. Migrate mailbox
  6. Assign Microsoft 365 licenses to users
  7. Changed so emails are routed directly to Microsoft 365
  8. Delete bulk migration batch
  9. Stop on-premises servers after completing post-migration tasks
  10. Guide users to start using

[User Task] Exporting/Importing emails

With POP, when past emails are downloaded to your computer, they are deleted from the server.

Emails received before migration to Microsoft 365 exist only locally, so in order to migrate, you need to export the emails from your computer and import them in the new email environment.


  1. Start Outlook and click “File” → “Open/Export”
  2. Click “Import/Export”
  3. Select “Export to file” and click “Next”
  4. Select “Outlook Data File (.pst)” and click “Next”
  5. Select the mail folder to export and click “Next”
  6. Choose a file location and options and click Done
  7. Set the password and click “OK”
  8. Export complete


  1. Start Outlook and click “File” → “Open/Export”
  2. Click “Import/Export”
  3. Select “Import from another program or file” and click “Next”
  4. Select “Outlook Data File (.pst)” and click “Next”
  5. Select the file to import and options, then click Next
  6. Enter the password set at the time of export and click “OK”
  7. Click “Finish”

Microsoft 365 makes it easy to move your computer

Once data is migrated to Microsoft 365, there will be no data migration work for server replacement.

In addition, the cloud environment also simplifies the task of replacing computers used by users.

Because Microsoft 365 stores your data in the cloud, you can access your data in the same way from any device by signing in with your account.

When replacing a computer, all you have to do is install Microsoft 365 on the new computer and sign in, so it is completed with simple work on the user side.

With Microsoft 365, you can use up to 5 computers at the same time, so disable it after you finish using your old computer. If possible, you should also uninstall it from your computer.

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User PC replacement flow

  1. Sign in to ( ) on your new computer
  2. Download the installer to your computer from “Install Office”
  3. Install Office by running the installer
  4. Launch an Office app, sign in, and activate
  5. Click your user icon and click Microsoft Account (or View Account)
  6. Click “Devices” to view installed devices
  7. Select your old computer and “Disable device”

Article Summary

  • There are a wealth of tools for migrating to Microsoft 365
  • Migration tools provided by Microsoft are license-free
  • Paid tools are recommended for advanced migration work and efficiency
  • Mailbox migration method depends on current mail environment
  • After migrating to Microsoft 365, it will be easier for users to replace their PCs

Using the cloud eliminates the need for regular data migration in the future, which is a big advantage.

Only the initial migration work is difficult, but in order to obtain a comfortable cloud environment, try using migration tools and support.