Why You Might Need a Migration Tool
Migrating mailboxes between Exchange Server and Microsoft 365 tenants is one of those tasks that tends to surface during company mergers, divestitures or when moving from on‑premises infrastructure to the cloud. Without automation, you’re left juggling PowerShell scripts, manual mailbox mapping and a great deal of downtime. To see if Stellar Migrator for Exchange could simplify this process, I tested the tool in a live environment and this review walks through the setup, performance, and features I found most useful.
Installation and Setup
Installing the Migrator for Exchange took only a few minutes. I downloaded the installer from Stellar’s website and ran it on a Windows 10 machine. The wizard prompts you to accept the license agreement, choose a destination folder and create shortcuts. On a system with at least 8 GB of RAM, I experienced no issues with the installation or initial launch. You don’t need an existing Exchange server on the host machine, since the tool runs independently from your Exchange environment.
Creating a Migration Job
Once launched, the application opens a wizard‑style interface. Your first task is to name the job and choose the source and destination platforms. In my case I migrated from Microsoft 365 to Microsoft 365, but you can also select Exchange Server on either side. There’s an option to load a CSV of pre‑mapped mailboxes to save time when dealing with large migrations.
Connecting to the Source and Destination
The next wizard step connects the tool to your source tenant. Migrator for Exchange registers itself in Entra ID and automatically assigns Microsoft Graph API permissions. It then prompts you to sign in with a global admin account to grant consent. A similar process connects the destination tenant. This automatic app registration means you don’t have to manually configure Azure AD permissions, reducing the chance of configuration errors.
Loading and Listing Mailboxes
After authentication, the wizard lists all primary mailboxes discovered in the source tenant. If you have more than 100 mailboxes, you can choose to load them via CSV. For my test, the tool retrieved 100 primary mailboxes and displayed them in a scrollable list. Each mailbox can be selected individually or loaded in bulk via CSV for larger projects.
Mapping Mailboxes
The mapping screen automatically matches source mailboxes to destination mailboxes by comparing email addresses and display names. Unmatched mailboxes are flagged in red, while matched pairs appear in green. You can edit mappings manually or import a CSV to define mappings exactly. The interface provides a search bar and priority column so you can reorder or find specific mailboxes quickly.
Performance and Concurrency
Migrator for Exchange lets you specify how many mailboxes to migrate concurrently (up to ten). In my environment I tested with four mailboxes in parallel. The application remained responsive, and the network bandwidth became the main bottleneck rather than the tool itself. There’s an option to pause and resume migrations, and if any mailbox fails you can rerun only the failed mailbox without starting over.
Additional Features
Beyond the basic workflow, several features make the tool stand out:
- Cross‑forest, cross‑domain and tenant‑to‑tenant migrations without establishing trust relationships
- Zero downtime with incremental (delta) migrations that transfer only new or changed items after the initial cutover
- Date‑range and folder filters for selective migration of specific content
- Support for migrating public folders and archive mailboxes alongside primary mailboxes
- Bulk mailbox mapping via CSV for large organisations and the ability to prioritise critical mailboxes
- Runs entirely on your local machine – no mailbox data is transmitted through Stellar’s servers
Licensing and Editions
Stellar Migrator for Exchange is licensed on a per‑mailbox basis. You can trial the software on up to two mailboxes for free, which is helpful for proof‑of‑concept testing. Paid licences start around US $7 per mailbox when migrating fifty or more mailboxes, with volume discounts available. While this pricing can add up for very large migrations, the time saved compared to manual methods often justifies the investment.
Final Thoughts
Stellar Migrator for Exchange delivers a clean, guided experience for moving mailboxes between Exchange and Microsoft 365. Its automation of app registration and mailbox mapping removes much of the complexity that normally accompanies these projects. It supports precise mailbox mapping, minimizes manual effort, and reduces the risk of migration errors. The tool’s intuitive interface, clear progress tracking, and consistent performance make it an excellent choice for small to medium-sized migrations, ensuring a smooth, efficient, and stress-free transition from start to finish.