Step 1: Inventory before you move anything
Migrations go wrong because of what nobody wrote down. Time spent here makes every later step shorter, and the list becomes your test plan on cutover day.
- People and mailboxes. Every user, shared mailbox, room and equipment calendar, distribution list and alias, each with a named owner.
- Data volume and archives. Mailbox sizes, archive mailboxes and PST files on laptops or file shares. PST files are easy to forget and slow to import.
- Everything that sends email. Scanners, accounting and practice management software, website forms, and alarm or monitoring systems. Note how each one sends mail today.
- Files and permissions. File shares, their sizes and who has access. Mark folders nobody has opened in years for archiving rather than migration.
- DNS and domains. Who controls your DNS, every domain you send mail from, and the current MX, SPF, DKIM and DMARC records.
- Devices. Laptops and phones that will need new mail profiles, and whether they will be managed after the move.
Before you finalize the list, ask every team lead three questions: what would stop your team working on the first morning, what do you regularly share with people outside the company, and which old files do you genuinely still need? Their answers usually surface a shared mailbox, a client folder or an app nobody else knew about.
Decide what not to migrate
Moving old data is not free: it slows the migration and clutters search. Agree a cut-off date with each department, archive the rest and keep the archive retrievable.
