Google Workspace to Microsoft 365 Migration Project Plan

A clean migration breaks into seven phases. Smaller projects compress some of these into a single afternoon; large enterprise moves may spend a week on each. The order stays the same either way.

Phase 1: Discovery and Assessment

Before you touch a single setting, you need an accurate picture of what you are moving. Inventory every user account. Record mailbox sizes, because a handful of 40 GB mailboxes will drive your timeline more than a hundred small ones. Note which accounts hold Google Contacts, Calendar events, and Tasks, since all of these carry over and each adds to the transfer. Deliverables for this phase are a mailbox inventory spreadsheet, a total data-size estimate, and a list of anything unusual: delegated mailboxes, forwarding rules, or heavy calendar sharing that will need attention later.

Phase 2: Planning and Design

With the inventory in hand, make the decisions that shape the rest of the project. Choose your migration approach: a single big-bang cutover for small teams, or a staged, batch-by-batch rollout for larger organizations. Decide how mailboxes map from the source to the target, whether same-name accounts pair automatically or need a custom mapping file. This is also where you set the target design in Microsoft 365. Confirm licensing so every destination mailbox has a plan assigned, and decide whether primary mail, archives, and shared mailboxes all land in their matching container. Reviewing the available Google Workspace migration scenarios helps you match your environment to a proven path.

Phase 3: Preparation and Configuration

Now you build the connections. On the source side, this means creating a service account in the Google Cloud Console, enabling domain-wide delegation, and authorizing the API scopes for Gmail, Contacts, and Calendar. The full sequence is documented in the Google Workspace admin configuration guide, and it is worth following exactly, since a missing scope is the single most common reason a first connection fails. On the target side, prepare the Microsoft 365 tenant and register the migration application for OAuth 2.0 modern authentication. The steps to connect to the target Office 365 walk through both automatic and manual app registration. Confirm your bandwidth is sufficient for the data volume you sized in Phase 1, and check the system requirements for the machine running the migration.

Phase 4: Pilot Migration

Start with a small pilot group of five to ten mailboxes that represents your real environment: one large mailbox, one with heavy calendar use, and a couple of ordinary users. Run the full migration for this group and then validate carefully. Log in to the target mailboxes and confirm that folder structure, labels, attachments, contacts, and recurring calendar events all arrived intact. The pilot is where you tune batch sizes and settle any mapping questions. Fix what breaks here, while the blast radius is ten people instead of the whole company.

Phase 5: Full Migration

Once the pilot passes, scale up. Group the remaining mailboxes into batches sized to your bandwidth and support capacity, and migrate them on the schedule you set in Phase 2. EdbMails processes multiple mailboxes concurrently, so large batches finish in hours rather than days. For organizations moving hundreds of accounts at once, see bulk Google Workspace mailbox migration for how EdbMails runs these batches without requiring individual user credentials. Keep the source environment live during this phase. Users continue working in Google Workspace while the transfer runs in the background, which is what makes a zero-disruption move possible.

Phase 6: Cutover and DNS Changes

Cutover is the moment new mail starts flowing to Microsoft 365. Just before the switch, run an incremental migration pass to catch every message and calendar entry that arrived since the last full run. Because incremental transfers move only new or changed items, this final sync is fast and adds no duplicates. Then update your domain's MX records to point at Microsoft 365 and adjust the Autodiscover record so Outlook clients connect to the new mailboxes. Schedule this for a low-traffic window, communicate it to users in advance, and allow time for DNS propagation.

Phase 7: Post-Migration Validation

The project is not finished when the last mailbox copies. Confirm mail flow in both directions from a sample of accounts. Have users set up their Outlook profiles and verify that calendars, contacts, and shared mailboxes all appear correctly. Keep the migration reports from each run as your record of what transferred, which mailboxes reported errors, and item counts per folder. Those reports are your evidence for audit and management sign-off.