Gmail to Outlook Migration

Migration Paths

Assess the source environment first:

Pre-Migration Checklist

Run through this with the client before touching anything:

• Inventory — Number of users, total mailbox sizes, largest mailbox, shared mailboxes, Google Groups
• Microsoft 365 plan — Confirm active subscription, verify admin access (Global Admin required)
• Source admin access — Google Workspace Super Admin + service account for bulk migration
• DNS access — Whoever manages MX records (registrar, Cloudflare, etc.)
• Data scope — Email only? +Contacts? +Calendars? +Drive files?
• Cutover window — When to switch MX records (weekend recommended)
• Client communication — Draft email to users about the switch, new login instructions
• 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

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

Execution

• Add users to migrate (CSV upload for bulk: source_email,destination_email)
• Start migration — Microsoft handles delta sync automatically
• Monitor progress in Admin Center → shows per-user status
• 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

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

Import to Outlook

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

Method 3: IMAP Bridge (Manual / Small Scale)

For personal Gmail accounts or when other methods fail:

• Enable IMAP in Gmail: Settings → Forwarding and POP/IMAP → Enable IMAP
• Create app password for Gmail account
• In Outlook desktop, add Gmail as IMAP account using app password
• Set up Microsoft 365 account in same Outlook profile
• Drag-and-drop folders from Gmail IMAP to Microsoft 365 mailbox

Data Mapping Considerations

DNS / MX Cutover

After migration data is transferred:

• Verify domain in Microsoft 365 Admin Center (TXT record)
• Update MX records to Microsoft:

Priority  Host
   0         company-com.mail.protection.outlook.com

• Set SPF: v=spf1 include:spf.protection.outlook.com ~all
• Set DKIM: Admin Center → Defender → Email authentication → Enable DKIM
• Set DMARC: v=DMARC1; p=none; rua=mailto:[email protected] (start with p=none)
• Autodiscover CNAME: autodiscover.outlook.com
• TTL: Lower TTL to 300 before cutover, restore to 3600 after 48h

Post-Migration Validation

Run these checks for every user:

• [ ] Email receiving on Outlook (send test from external)
• [ ] Historical emails present (spot-check oldest + newest)
• [ ] Folders mapped correctly (labels→folders)
• [ ] Contacts imported (check count vs Google)
• [ ] Calendar events present (check recurring events specifically)
• [ ] Google Groups recreated as Distribution Lists
• [ ] Signatures set up in Outlook
• [ ] Mobile devices re-configured (Outlook app or Exchange)
• [ ] Gmail IMAP disabled or account removed

Common Issues

Deliverables Template

For client-facing migration projects, prepare:

• Migration Plan — Timeline, phases, user batches, rollback plan
• User Communication — Email template announcing the switch
• Admin Runbook — Step-by-step for the migration operator
• Validation Report — Per-user sign-off checklist