Moving to Microsoft 365 without the downtime

Moving a small business to Microsoft 365 should feel like moving into a new office on a long weekend, not like being evicted. Here is the checklist we run, in the order that keeps the lights on.

Before anything moves

1. Inventory the accounts. Every mailbox, shared mailbox, alias, and distribution list. The surprises here are always the same: the owner’s email is actually a personal Gmail, and someone has been forwarding payroll to an ex-employee’s account since 2022.
2. Check the domain. Who owns the domain, who controls DNS, and can you log into both? More migrations stall at DNS than at anything technical.
3. Decide the cutover date and the rollback point. Email migration is reversible for days if you keep the old mailboxes alive in parallel. Plan for that.

The migration itself

• Mail first. Migrate mailboxes with overlapping delivery so nothing bounces during the transition.
• Files second. Shared drives become Teams and SharePoint libraries. Move folder by folder, and let staff keep working from the old location during the transition.
• Phones last. Teams calling or a hosted phone system goes in once everyone is comfortable with the new identity.

The week after

Walk the floor. The real test is not the migration report, it is whether the accounts payable person can still print cheques, whether the shared calendar still books, and whether anyone has quietly been using a personal Dropbox for client files. Fix those in week one, before they harden into habits.

A migration done right is boring. The only people who notice are the ones who used to lose an afternoon to a crashed Outlook profile.