Microsoft rebranded Office 365 as Microsoft 365, and the migration playbook changed with it. You still move mail, files, identities, and apps into the cloud, but the admin portals, sync tools, and collaboration stack have new names. This checklist walks through a practical Microsoft 365 migration in three phases: plan, prepare, and cut over.

If you still see “Office 365” on invoices or older docs, that is normal. Microsoft kept some legacy SKU labels. For planning and admin work in 2026, treat the destination as Microsoft 365 and use the current Microsoft 365 admin center.

Why teams move to Microsoft 365

Microsoft 365 is a per-user subscription that bundles Office apps (Word, Excel, PowerPoint, Outlook), cloud email (Exchange Online), file storage (OneDrive and SharePoint), and teamwork (Teams). You scale seats as the company grows instead of buying servers and perpetual licenses up front.

The practical upsides for most small and midsize teams:

Work from Windows, Mac, browsers, and phones with the same mailbox and files
Coauthor documents in real time instead of emailing attachments
Central identity and licensing in the Microsoft 365 admin center
Built-in security baselines (MFA, Conditional Access on eligible plans) that are hard to match on aging on-prem setups

Pick the plan that matches how people work (Business, Enterprise, Education, and so on). Do not buy seats until you know mailbox counts, file volume, and whether you need hybrid identity.

Match apps to how people actually work

Before you migrate anything, map workloads to the people who use them.

Individuals

Most people need Outlook, Word/Excel/PowerPoint (desktop or web), OneDrive, and Teams chat. Ask what they open every day, then keep that list short.

Departments

Shared mailboxes, SharePoint team sites, and Teams channels usually replace shared drives and distribution-list chaos. Decide ownership for each shared resource before cutover day.

Company-wide

Intranet pages, company-wide Teams, retention policies, and DLP sit at the org level. Plan those with IT and compliance together so you are not inventing policy after mail is already in the cloud.

Step 1: Plan the Microsoft 365 migration

Gather facts about the current environment first. Surprises during cutover are expensive.

Get people on board

Hold a short kickoff with managers and power users. Share the go-live window, what will change (new sign-in, new Teams instead of old chat tools), and where people can ask for help.

Inventory your infrastructure

Document the pieces that affect mail and identity:

Servers and Exchange or other mail systems
Authentication (Active Directory, federation, MFA)
Bandwidth and VPN paths used during migration
Certificates and public DNS
Client apps and mobile device management
Mail routing (MX, connectors, spam filters)
Mail archiving and compliance holds

Microsoft’s readiness and migration docs are a good checkpoint: start with the Exchange Online mailbox migration overview and the Microsoft 365 enterprise overview.

Write a migration agenda

List tasks in order: tenant setup, domain verify, identity sync, pilot users, mailbox batches, file migration, DNS cutover, then decommission. Put owners and dates on each line.

Choose a mailbox strategy

Common paths include cutover, staged, and hybrid (including minimal hybrid) migrations into Exchange Online. Pick based on mailbox count, whether you must keep on-prem Exchange for a while, and how long coexistence needs to last. Microsoft documents these options in the mailbox migration guide linked above.

Size the mailboxes

Export item counts and mailbox sizes. Large mailboxes slow batches. Archive or purge junk before you migrate so you are not paying to move trash.

Decide which files move

Inventory file shares, home drives, and existing SharePoint or Google Drive content. Decide what goes to OneDrive (personal) vs SharePoint or Teams (shared). If you are leaving Google Drive, our Google Drive to OneDrive sync guide covers a practical bridge for individuals.

Plan identity and provisioning

Choose cloud-only accounts or hybrid identity. For hybrid, plan on Microsoft Entra Connect (formerly Azure AD Connect / Directory Sync) or Microsoft Entra Cloud Sync. Clean UPNs so users sign in with a real email-style address, not a .local domain.

Test bandwidth

Run a sample mailbox or file batch and measure how long it takes. Use that number to schedule overnight or weekend waves.

Cover phones and tablets

List the mobile platforms in use (iOS, Android). Plan Outlook mobile or the built-in mail apps, plus how you will push Teams and OneDrive. Company-owned devices may need Intune or another MDM enrollment step before day one.

Write the user communications plan

Send dated notices: what changes, when passwords or MFA prompts appear, and where to get help. Include a one-pager for installing the Office apps. Point people to our Microsoft 365 install guide for Windows and Mac so they are not guessing at the download page.

Step 2: Prepare the environment

Clean the source environment before you sync or move data.

Get help if you need it

Directory cleanup, hybrid Exchange, and DNS cutovers are where migrations usually stall. If your team has never run one, budget for a Microsoft partner or experienced admin. Skipping this step to “save money” often costs more in downtime.

Verify your domain in Microsoft 365

In the Microsoft 365 admin center, open Setup (or Settings) > Domains, add your company domain, and prove ownership with the TXT (or MX) record Microsoft shows you. Follow Microsoft’s add a domain steps. Do not flip MX to Microsoft until mailbox migration is ready, unless your chosen migration method requires it.

Clean up Active Directory

Fix duplicate proxies, invalid characters, empty required attributes, and stale accounts. Tools like IdFix still help catch directory problems before sync.

Plan single sign-on and MFA

Modern Microsoft 365 sign-in is Microsoft Entra ID. Enable MFA for admins first, then users. Federation (AD FS) is optional; many orgs run cloud authentication with Entra Connect sync instead of full federation.

Install Microsoft Entra Connect (directory sync)

If you need hybrid identity, install and configure Microsoft Entra Connect on a supported Windows Server, choose your sync scope, and verify that users appear in Entra ID before you assign licenses. Keep the sync engine on a supported version; Microsoft publishes mandatory upgrade deadlines for Entra Connect Sync.

Configure mail coexistence if required

For hybrid Exchange, run the current Hybrid Configuration Wizard so on-prem Exchange and Exchange Online can coexist during batches. See Microsoft’s Exchange hybrid documentation.

Turn on SharePoint and OneDrive

Create the SharePoint sites and Teams you planned. Prepare Migration Manager or the SharePoint Migration Tool if you are moving file shares or old SharePoint content. Microsoft’s SharePoint and OneDrive intro for admins is a solid starting point.

Set up Microsoft Teams (not legacy IM)

Older Office 365 checklists talked about “Online IM” and Skype for Business. For new migrations, standardize on Microsoft Teams for chat, meetings, and channel files. Pilot a few teams before company-wide rollout.

Update clients and install Microsoft 365 Apps

Push current Microsoft 365 Apps (Click-to-Run) to Windows and Mac endpoints, or give users the install steps from our guide. Retire ancient Office MSI installs that fight Click-to-Run.

Step 3: Finalize the cutover

Move production data only after pilot users succeed.

Assign licenses

Assign Microsoft 365 licenses in the admin center so Exchange Online, Teams, SharePoint, and OneDrive provision for each user before their batch moves.

Tell people the cutover details

Send the final notice with the exact date, expected downtime (if any), MFA enrollment steps, and help desk contacts.

Migrate mailboxes

Run your chosen Exchange migration batches. Shrink oversized mailboxes first if a batch is crawling. Watch the migration dashboard until each batch shows Completed.

Move files and folders

Migrate file shares and personal data into OneDrive/SharePoint with your selected tool. Spot-check permissions on a few sensitive folders.

Update DNS records

When mailboxes are ready, update MX, Autodiscover, SPF, DKIM, and DMARC at your DNS host so mail flows to Microsoft 365. Keep a rollback note with the previous values for 48 hours.

Configure devices

Help users add their Microsoft 365 account on phones and tablets, or push profiles through MDM. Confirm they can open mail, Teams, and OneDrive files off the corporate network.

Run post-migration tests

From outside the office network, test: send/receive mail, open a shared SharePoint file, join a Teams meeting, and create a new Word doc in OneDrive. Fix failures before you decommission old servers.

Check critical Office templates

Open your most-used Word, Excel, and PowerPoint templates. Confirm macros, fonts, and layouts still work under Microsoft 365 Apps. Fix anything broken before you call the project done.

When the tests pass, you are on Microsoft 365. Keep the old environment read-only for a short safety window, then decommission on a scheduled date.