Microsoft 365 migrations are routine, but the details decide whether users notice a smooth switch or a week of missing email.
Before you move anything
- Licensing: map every user to the right plan and identify shared mailboxes, which need no licence.
- Domain: verify it in Microsoft 365 and plan DNS changes, including SPF, DKIM and DMARC.
- Identity: decide between syncing an on-premise directory or going cloud-only.
- Security: enable multi-factor authentication from day one.
Moving mail and files
- Run a pilot with a small group, including at least one demanding user.
- Migrate mail in stages and communicate the cut-over date clearly.
- Keep the old system read-only for a defined period.
- Move files to SharePoint and OneDrive after mail, with a folder and permission structure agreed in advance.
After cut-over
Configure security baselines: conditional access, anti-phishing policies, data loss prevention where needed and a third-party backup. Then train users on Teams, OneDrive sharing and the mobile apps.
Choosing the right plans
| Need | Plans to consider |
|---|---|
| Email and Teams only, browser apps | Business Basic |
| Desktop Office apps plus email and Teams | Business Standard |
| Advanced security, device management, DLP | Business Premium |
| Over 300 users or advanced compliance | Enterprise plans |
| Shared inboxes like sales@ or support@ | Shared mailbox, no licence needed within size limits |
Mixing plans is allowed and usually saves money: give Business Premium to admins and finance, and lighter plans to staff who only need email and Teams.
Common migration mistakes
- Changing MX records before mailboxes are ready, so mail bounces.
- Forgetting phones and tablets, which then keep syncing to the old server.
- Copying file shares as-is, including years of broken permissions.
- Skipping DMARC, leaving the domain open to spoofing.
