We're moving from Exchange Server 2016 on-prem to Microsoft 365. About 80 mailboxes, ranging from 2GB to 18GB each.

Need to keep shared mailboxes, distribution lists and public folders intact. Downtime has to be minimal. What's the most reliable approach at this scale?

At 80 mailboxes you've got a couple of realistic options.

Microsoft's native hybrid migration is solid but it means setting up a hybrid Exchange environment first, which takes real configuration time. Fine if you have an experienced admin, annoying if you don't.

SysTools Office 365 Migration does Exchange to M365 without the hybrid setup. Shared mailboxes, public folders and distribution lists all come across fine. Worth looking at if the hybrid config is putting you off.

Before either route: audit mailbox sizes, archive or delete old mail to cut transfer time. Set your MX record TTL to 3600 a week before cutover so the DNS switch happens fast.

Hybrid was what our IT consultant pushed too but none of us were excited about the setup time. Checking out the SysTools option now. Does it handle calendars and contacts as well, or just mail?