Looking for some input from folks who've actually gone through this. We're preparing for a business-wide tenant-to-tenant migration in the next couple of months (roughly 300+ mailboxes, mix of regular users, shared mailboxes, and a few large archive accounts), and I want to avoid the common mistakes I keep seeing mentioned in other threads — flattened folders, broken permissions, and painful downtime during cutover.

While researching options, I came across this DRS Softech Tenant to Tenant Migration Tool , which seems to cover most of what we need for a business-scale migration — batch/bulk mailbox migration, folder structure preservation, shared mailbox and permission handling, plus incremental/delta migration so we're not stuck redoing work if something gets interrupted mid-project. The pre-migration reporting feature also looks useful for catching licensing or mapping issues ahead of time rather than during the actual cutover weekend.

Before committing, I wanted to check if anyone here has used it (or something similar) for a business migration of comparable size, and how it performed in terms of speed, support responsiveness, and whether folder/permission structures actually came through intact on the other end.