Best third party migration tool

We’ve used a few different tools for Microsoft 365 tenant-to-tenant migrations over the years, and honestly the “best” one usually depends on the project size, complexity, and budget. For smaller to mid-sized Office 365 migrations, I had a reasonably good experience with EdbMails Office 365 Migration.

What I liked was that it handled mailbox migrations, archive mailboxes, permissions, and incremental syncs in a fairly straightforward way without requiring a very complicated setup. The UI was easier for junior admins compared to some enterprise migration platforms, and the pause/resume capability was useful during throttling or network interruptions. We also used it for staged migrations where users were moved in batches over time.

That said, like any migration tool, it’s not perfect. Microsoft throttling, source mailbox issues, and large tenant migrations can still slow things down regardless of the product being used. I’d still recommend testing with a pilot batch first before committing to any migration platform.

For very large enterprise projects with complex coexistence requirements, some organizations may prefer higher-end migration suites, but for standard Office 365 mailbox migration scenarios, EdbMails worked reasonably well in our case.

We don't recommend third-party tools here, as it quickly turns into a spam fest with representatives from the different vendors. There are several tools, look them up, check their product descriptions, etc. There are also multiple reviews/articles out there written by independent consultants, which you can trust more than the marketing fluff you'll get from most vendor's pages. 

If you care mostly about Exchange, I'd recommend sticking with a vendor that has a proven history in that space.