Gmail to Outlook Migration

Migration Paths

Assess the source environment first:

Pre-Migration Checklist

Run through this with the client before touching anything:

1. Inventory — Number of users, total mailbox sizes, largest mailbox, shared mailboxes, Google Groups
2. Microsoft 365 plan — Confirm active subscription, verify admin access (Global Admin required)
3. Source admin access — Google Workspace Super Admin + service account for bulk migration
4. DNS access — Whoever manages MX records (registrar, Cloudflare, etc.)
5. Data scope — Email only? +Contacts? +Calendars? +Drive files?
6. Cutover window — When to switch MX records (weekend recommended)
7. Client communication — Draft email to users about the switch, new login instructions
8. Retention — Keep Google Workspace active 30 days post-migration as safety net

Method 1: Microsoft Data Migration Service (Recommended for Google Workspace)

Best for org-wide migrations from Google Workspace to Microsoft 365.

Setup

1. Microsoft 365 Admin Center → Migration → Data Migration
2. Select Google Workspace as source
3. Create service account in Google Admin Console with domain-wide delegation
4. Upload service account key file to Microsoft migration tool
5. Select what to migrate: Email, Contacts, Calendars
6. Choose date range filter (optional — migrate only last N months to save time)

Execution

1. Add users to migrate (CSV upload for bulk: source_email,destination_email)
2. Start migration — Microsoft handles delta sync automatically
3. Monitor progress in Admin Center → shows per-user status
4. Migration runs in background — users can keep using Gmail during this phase

CSV Format

source_email,destination_email
[email protected],[email protected]
[email protected],[email protected]

See references/csv-template.md for full template with notes.

Method 2: Google Takeout + Outlook Import

Best for individual users or when bulk migration fails.

Export from Google

1. Go to Google Takeout: https://takeout.google.com
2. Select Mail, Contacts, Calendar
3. Choose MBOX format for mail (compatible with Outlook)
4. Download archive when ready (can take hours/days for large mailboxes)

Import to Outlook

1. Email: Outlook Desktop → File → Open & Export → Import/Export → Import from MBOX
2. Contacts: Import Google CSV to Outlook contacts
3. Calendar: Export Google Calendar as ICS, import to Outlook Calendar

Limitations: Manual per-user process, requires desktop Outlook, size limits.

Method 3: IMAP Bridge (Manual / Small Scale)