How to Migrate Exchange Server to Microsoft 365: A Hands-On Test – Stellar Migrator for Exchange

Published on: 26/10/2026 | Updated on: October 26, 2026

Migrating email from an on-premises Microsoft Exchange Server to Microsoft 365 involves more than copying emails. You must connect both environments, map source mailboxes to their intended destinations, configure migration settings, run the migration, and verify the results.

In this hands-on review, we demonstrate the Exchange Server to Microsoft 365 migration workflow using Stellar Migrator for Exchange. We follow a real test scenario involving an on-premises Exchange mailbox and a Microsoft 365 destination mailbox. We also examine the migration report, review the target mailbox in Outlook, and explain how to interpret successful, previously migrated, and failed items.

Our test uses dummy email messages. This makes it possible to examine the migration workflow without relying on real business correspondence as test content.

Quick Summary

• Migration type: On-premises Exchange Server to Microsoft 365
• Migration software: Stellar Migrator for Exchange
• Test content: Dummy emails and mailbox folders
• Migration scope: All items and all folders
• Reported results: 408 items processed, including 2 newly migrated items and 406 previously migrated items.
• Verification method: Migration report and Outlook mailbox inspection

The source and destination addresses are intentionally different in this test. So that the contents of the Jose mailbox be migrated into the Alice mailbox.

What Is Exchange Server to Microsoft 365 Migration?

Exchange Server to Microsoft 365 migration is the process of transferring mailbox data from an organization’s on-premises Exchange environment to Exchange Online, the cloud email service included with Microsoft 365.

Depending on the migration method and the source environment, the process may involve email messages, folders, calendars, contacts, tasks, and other supported mailbox items.

Organizations may migrate to Microsoft 365 to reduce the work involved in maintaining on-premises email infrastructure, support remote access, or consolidate their email services in the cloud.

A successful migration requires more than a completed progress indicator. Administrators should check that each source mailbox is mapped to the correct destination. They should also confirm that important data is present. Finally, they should review any failed items.

Requirements

Before starting the migration, ensure you have the following:

• An accessible on-premises Microsoft Exchange Server with the source mailboxes available for migration.
• A Microsoft 365 tenant with the destination mailboxes created and accessible.
• The necessary permissions and authentication credentials to connect to both the source Exchange Server and Microsoft 365.
• Stellar Migrator for Exchange installed on a supported Windows computer.
• Network connectivity from the computer running the software to the source Exchange Server and Microsoft 365 services.
• Sufficient available mailbox storage in Microsoft 365 to accommodate the data being migrated.

The exact permissions and connection requirements depend on the Exchange version, Microsoft 365 configuration, and the migration software version. Confirm the requirements for your environment before starting.

How to Migrate Exchange Server to Microsoft 365 Using Stellar Migrator for Exchange

In this hands-on test, we use Stellar Migrator for Exchange to migrate mailbox data from an on-premises Exchange Server to Microsoft 365. The process includes software installation, server connections, mailbox mapping, migration settings, and destination verification.

To get started with Stellar Migrator for Exchange, we first registered through the official Stellar Migrator for Exchange website. After completing the registration process, we received a welcome email containing the login credentials and the information required to access the software.

The email included a download link for the Stellar Migrator for Exchange installer (EXE) and access details for the Stellar Licensing Portal, available at stellarlicenseserver.com.

We downloaded the software installer using the link provided in the email. Alternatively, users can access the download through the Licensing Portal.

Step 1: Install Stellar Migrator for Exchange

Download Stellar Migrator for Exchange from the official website.

1. Download the installer for your Windows computer.
2. Run the installer.
3. Follow the installation wizard to complete the setup.
4. Launch Stellar Migrator for Exchange.

Use the version and system requirements appropriate for your environment. Make sure the computer can reach both the on-premises Exchange Server and Microsoft 365.

Welcome Screen

The welcome screen offers two options: Login using your registered credentials or Continue without login to explore the software. A Help option is also available for assistance.

Sign In to Licensing Server

Enter the email address and password received during registration, then click Login. You can select Remember me to save your credentials or use Forgot password? to reset your password.

Connected to Licensing Server

After successful login, the software displays your available migration licenses. Click Create Job to start a new migration or Open Job to resume an existing one.

2. In the Migration Type section, choose the appropriate source and target server types: Exchange Server as the source and Microsoft 365 as the target.

The selected migration type determines which source and target connection settings are available in the subsequent steps.

Step 3: Enter the Job Name

In the General tab, enter a descriptive name for the migration job.

For our test, the job name was Migration 1.

A clear name helps administrators identify the job when reviewing its settings, progress, and reports. For a production migration, consider including the project name, environment, or migration date.

Select the mailbox type(s) you want to migrate: primary/shared mailboxes, archive mailboxes, or public folders. You can also import a pre-mapped CSV file directly from this screen.

Continue to the source connection settings.

Step 4: Connect to the Source Exchange Server

In the Connect source section, configure the connection to the on-premises Exchange environment.

1. Enable Use Autodiscover email.
2. Enter the email address and password requested by the software.
3. Validate the source connection.
4. Continue only after the connection is accepted.

Then select the source mailbox and go next.

Step 5: Connect to Microsoft 365

Next, configure the destination connection.

1. Open Connect target.
2. Enter the Microsoft 365 account details requested by the software.
3. Validate the target connection.
4. Confirm that the connection succeeds before continuing.

The next screen shows the list of mailboxes found in the target (destination) server. If you cannot see all your target mailboxes, use ‘Load Mailboxes Using CSV’ to load the complete list. Review the mailboxes to ensure the destination accounts are available for mapping.

Step 6: Select and Map Mailboxes

Open Map mailboxes to match each source mailbox with its intended Microsoft 365 destination.

If the software maps mailboxes automatically, review the proposed matches. Edit a mapping when necessary to reflect the approved migration plan.

To change a mapping, use the edit control beside the relevant mailbox row and select the correct target mailbox.

For migrations involving multiple users, review every mapping before proceeding. An incorrect mapping can send data to the wrong destination mailbox.

Step 7: Configure the Scheduler

Open the Scheduler section and decide whether the job should run on a schedule or be started manually.

For our test, no schedule was configured. We planned to start the job manually after reviewing its settings.

Manual execution is useful for controlled testing because it lets the administrator review the configuration before starting the migration.

If you choose a scheduled run, confirm the intended date and time before continuing.

Step 8: Set the Date Filter

Open Date filter and choose Migrate all items if the goal is to migrate all items within the selected scope.

This setting avoids intentionally restricting the migration to a specific date range.

Confirm the selected option before proceeding.

Step 9: Choose Folder Types

Open Folder type filter and select the mailbox data types that should be included.

Depending on the available options and migration requirements, these may include:

• Emails
• Contacts
• Calendars
• Tasks
• Notes
• Journals
• Junk email
• Deleted items
• Drafts

Choose the required types rather than assuming every organization needs every item type.

In our test, all available folder types were selected. However, the five Journal items that later failed were not required for the client’s migration objective.

Step 10: Configure Maximum Concurrency

Open Max concurrency to configure the number of simultaneous mailbox and item migration threads.

For our test, we recommend starting with a concurrency setting of 5, as suggested by software.

A conservative setting is a practical starting point for a controlled test. It may help limit simultaneous workload while you observe the migration’s behavior. It does not guarantee that the migration will be faster or prevent every connection problem.

Use the settings supported by your software version and adjust them only after evaluating performance, available resources, and server responsiveness.

Step 11: Review the Migration Summary

Open Summary and review the configuration before creating the job.

Check the following:

• Source server type and connection account
• Microsoft 365 target connection
• Total number of mailboxes selected
• Source-to-target mailbox mapping
• Scheduler settings
• Date filter
• Folder type filter
• Maximum concurrency

For our test, the summary showed one mapped primary mailbox, all items selected, all folders selected, no scheduler, and one concurrent mailbox.

Make sure the source and destination mapping matches the client’s instructions. If you find an error, return to the appropriate section and correct it before continuing.

When the summary is correct, click Finish to complete the job setup.

At this stage, verify that the migration job has been created successfully. Do not assume that clicking Finish has necessarily started the migration; the next step is to start the job from the application’s main job screen.

Step 12: Start the Migration Job

Return to the main screen and locate the migration job you just created.

1. Select the intended migration job.
2. Click Start.
3. Monitor the job’s status and progress.
4. Review the results after processing finishes.

In our test, the job was named Migration 1, and the selected mapping was Jose’s Exchange mailbox to Alice’s Microsoft 365 mailbox.

Avoid starting the wrong job or repeatedly rerunning an existing job without first checking its status and results.

Step 13: Review the Results and Verify the Destination

After the job finishes, inspect the migration report. Review total items, migrated items, filtered items, failed items, and items marked as already migrated.

Open migrated mailbox in Outlook and check representative messages, custom folders, attachments, and other required data. We also confirmed that the source mailbox contained the same dummy test emails visible in the destination’s Migration folder.

The migration report for our test showed the following results for selected folders:

Folder	Total items	Already migrated	Failed
Inbox	98	98	0
Sent Items	148	148	0
Calendar	39	39	0
Contacts	26	26	0
Drafts	2	2	0

The job summary also reported two items migrated during the run and 406 already migrated items.

Verify the Destination Mailbox in Outlook

A migration report is only one part of the verification process. The next step is to open the destination mailbox in Outlook and inspect its contents.

In our test, we opened Alice’s Microsoft 365 mailbox and located a folder named Migration. This folder contained dummy email messages created for migration testing.

Destination Verification Checklist

Use this checklist when validating the result:

• Confirm that the destination is Alice’s intended Microsoft 365 mailbox.
• Search for known messages from the source mailbox.
• Open sample emails and check their subjects, senders, dates, and bodies.
• Open attachments in representative messages.
• Verify that expected custom folders are present.
• Check Sent Items and other required folders.
• Compare source and destination message counts for matching folders.
• Check calendars, contacts, and other required item types.
• Review the migration report for failed items.
• Record any unresolved differences before declaring the migration complete.

For stronger verification, compare several known messages from different dates, including older and newer messages. If possible, compare message identifiers or other suitable attributes rather than relying on folder names alone.

Best Practices for Exchange Server to Microsoft 365 Migration

Before carrying out a production migration, follow these practices:

1. Document mailbox mappings. Confirm the destination for every source mailbox.
2. Test with a controlled mailbox. Use known messages and representative folders.
3. Review permissions. Ensure the source and target connections have the required access.
4. Confirm the migration scope. Decide whether to include all folders and item types.
5. Preserve recovery options. Keep appropriate backups and migration reports.
6. Monitor failed items. Investigate errors that affect required data.
7. Verify the destination independently. Use Outlook or another appropriate method to inspect the migrated mailbox.
8. Avoid unnecessary reruns. Review the current job status and understand the software’s retry behavior before restarting a completed job.
9. Obtain client approval. Confirm that the required data is present before signing off on a production migration.

Final Verdict

Stellar Migrator for Exchange, an Exchange migration tool, provided a structured workflow for connecting an on-premises Exchange Server to Microsoft 365, mapping a source mailbox to a destination, configuring migration settings, and reviewing folder-level results.

Our test demonstrated the practical steps involved and showed how the migration report can help identify items that require further attention.

The main lesson is that migration completion and migration verification are two different things. A completed job is useful evidence of processing, but it does not replace a comparison of the required source and destination data.

For IT administrators planning an Exchange-to-Microsoft 365 migration, the safest approach is to confirm every mailbox mapping, test with known data, review all failed items, and verify the target mailbox before declaring the migration successful.