This is the Master Migration Protocol for moving from Microsoft 365 (Exchange Online) to Google Workspace using the “New Data Migration Service” (DMS).

This method replaces the old “GWMME” (local server tool) and the basic IMAP fetch. It utilises a direct Cloud-to-Cloud connection via the Microsoft Graph API and EWS, authorised securely via OAuth.

Microsoft to Google Workspace Step1

Unlike older methods that required you to manually create Azure Apps and copy Client IDs, the new DMS automates the authorization.

1. Google Admin Preparation:

   • Log into Google Admin Console > Data > Data import & export > Data migration.

   • Look for the section labeled “Data Migration (New)” or “Exchange Online”.

   • Note: If you don’t see “New”, you may need to check “Data Migration” > “Set up new migration” and select “Microsoft 365” from the source dropdown.

2. Authorize Tenant Access:

   • Click Connect.

   • You will be redirected to a Microsoft 365 Login page.

   • Crucial: You must sign in with a Global Administrator account for the source Microsoft 365 tenant.

   • Accept the permissions request. This grants Google’s migration service specific “Read” scopes (Mail.Read, Calendar.Read, Contacts.Read) to your M365 tenant.

3. The “Throttling” Pre-Emptive Strike (Highly Recommended):

   • Even with the new API, Microsoft often throttles large data exports.

   • Action: Log into the Microsoft 365 Admin Center > Help & Support (bottom right).

   • Type: “EWS Throttling”.

   • Run the self-service diagnostic.

   • If it detects that throttling is enabled, choose the option to “Update” or “Temporarily Relax Throttling” for 30–90 days.

   • Impact: This can increase migration speed from ~0.5 GB/hour/user to ~2 GB/hour/user.

Microsoft to Google Workspace Step2

1. Select Data Types:

   • Email: Migrates messages, folders (converted to Labels), and attachments.

   • Calendar: Migrates primary calendars. Warning: Shared calendar permissions often need manual re-sharing after migration.

   • Contacts: Migrates personal contacts.

2. Identity Mapping (The CSV File):

   • You need a CSV file to tell Google which source email belongs to which destination email.

   • Format:

     Code snippet

     Source Email,Google Workspace Email
     john.doe@microsoft-domain.com,john@google-domain.com
     jane.smith@microsoft-domain.com,jane@google-domain.com
     

   • Upload this CSV in the “Add Users” or “Upload CSV” step of the DMS setup.

Microsoft to Google Workspace Step3

1. Start Migration:

   • Once the CSV is processed, click Start.

   • Status Indicators:

     • Initializing: Google is scanning the source mailbox structure.

     • In Progress: Data is flowing.

     • Sleep/Idle: Often happens if Microsoft imposes a temporary rate limit. Google will auto-retry.

2. The “Cutover” Weekend:

   • Friday Evening: Lower TTL on MX records to 5 minutes (as per the standard protocol).

   • Change MX Records: Point them to Google (ASPMX.L.GOOGLE.COM, etc.).

   • Sunday Night (The Delta Pass):

     • Go back to the migration job in Google Admin.

     • Do NOT stop or delete the migration.

     • Select all users and choose “Run Delta” or “Retry/Resume”.

     • What this does: It compares the source M365 mailbox with the Google mailbox and copies only the emails delivered between the start of the migration and the MX record change.

Technical Limitations