We are beginning to move departments from our local mail server to Microsoft Teams.
What’s the best way to do that?
In the first group there are roughly 90,000 files in 11,000 folders or 55 gb worth of data.
I’m assuming you meant local file server. In my opinion, one of best tools available is the free one from Microsoft - Sharepoint Migration Tool (aka SPMT). You’ll run this on your file server. Create an Excel/CSV defining what local folders go to what Sharepoint (Teams) libraries online. The tool does the rest. It has pretty good error reporting and supports re-syncing. So you may do one large batch at first with everything and get it moved, then do smaller jobs where you resync a team or two at a time to do a cutover.