Email Migration: Gmail to Exchange Online¶

Status: Authored 2026-04-30 Audience: M365 administrators, migration engineers, and IT leads executing Gmail to Exchange Online migration. Scope: All email migration methods, label mapping, filter conversion, delegation, and DNS cutover for Gmail to Exchange Online.

Overview¶

Gmail to Exchange Online migration is the highest-visibility workload in a Google Workspace to M365 migration. Users interact with email dozens of times daily, and any disruption is immediately noticed. Microsoft provides multiple migration methods, with the Google Workspace migration feature in Exchange Admin Center (EAC) being the recommended approach for full-fidelity migration of email, calendar, and contacts.

FastTrack recommendation: For organizations with 150+ seats, engage Microsoft FastTrack before starting. FastTrack engineers will configure and execute the migration at no additional cost. The information below is for organizations running migration independently or supplementing FastTrack.

Migration method selection¶

Decision matrix¶

Recommendation¶

For most organizations, the Google Workspace migration in EAC is the right choice. It is free, supports email + calendar + contacts, provides incremental sync, and is supported by Microsoft. Third-party tools add value for:

• Organizations needing fine-grained scheduling (migrate by department on specific dates).
• Environments with complex delegation and shared mailbox configurations.
• Migrations requiring detailed per-item error reporting.

Pre-migration preparation¶

1. Google Workspace configuration¶

Before migration can begin, configure Google Workspace to allow M365 to access mailbox data.

Create a Google Cloud project and enable APIs¶

1. Navigate to Google Cloud Console.
2. Create a new project (e.g., "M365 Migration").
3. Enable the following APIs:
   • Gmail API
   • Google Calendar API
   • Contacts API
   • Google Workspace Admin SDK
4. Create a service account with domain-wide delegation.
5. Download the service account JSON key file.

Grant domain-wide delegation¶

In Google Workspace Admin Console:

1. Navigate to Security > API Controls > Domain-wide Delegation.
2. Add the service account client ID.
3. Grant the following OAuth scopes:

https://mail.google.com/
https://www.googleapis.com/auth/calendar
https://www.googleapis.com/auth/contacts
https://www.googleapis.com/auth/admin.directory.user.readonly
https://www.googleapis.com/auth/gmail.readonly

2. Microsoft 365 preparation¶

Verify domain in M365¶

# Connect to Exchange Online
Connect-ExchangeOnline -UserPrincipalName admin@contoso.com

# Verify domain is added and verified
Get-AcceptedDomain | Format-Table DomainName, DomainType, Default

Create user accounts¶

Provision all users in Entra ID before starting migration. Users must have Exchange Online licenses assigned.

# Connect to Microsoft Graph
Connect-MgGraph -Scopes "User.ReadWrite.All"

# Verify users have Exchange Online licenses
Get-MgUser -All | Select-Object DisplayName, UserPrincipalName, AssignedLicenses |
    Format-Table -AutoSize

Configure migration endpoint¶

In Exchange Admin Center:

1. Navigate to Migration > Migration endpoints.
2. Click New migration endpoint.
3. Select Google Workspace.
4. Provide the service account email and JSON key file.
5. Test the endpoint connection.

Gmail label mapping strategy¶

Gmail labels are conceptually different from Outlook folders. Gmail allows multiple labels on a single message (like tags); Outlook uses a folder hierarchy where each message lives in exactly one folder.

Mapping rules¶

Handling multi-label messages¶

When a Gmail message has multiple labels (e.g., "Project-Alpha" and "Finance"), the migration tool places the message in the primary folder and applies additional labels as categories. The primary folder is determined by label priority (most specific label wins).

Recommendation: Before migration, audit heavy multi-label users and communicate the folder vs. category mapping. Most users adapt quickly, but power users with complex label taxonomies may need individual guidance.

Gmail filter to Exchange rule mapping¶

Per-user filters to Outlook rules¶

Gmail filters map to Outlook Inbox rules. Common mappings:

Migration approach: Gmail filters do not automatically migrate. Export filters per-user (Gmail Settings > Filters > Export) and recreate as Outlook rules manually or via PowerShell.

# Example: Create an Outlook rule via PowerShell
# (Exchange Online Management module)
New-InboxRule -Mailbox user@contoso.com `
    -Name "Project Alpha to Folder" `
    -From "pm@partner.com" `
    -MoveToFolder "Project-Alpha" `
    -StopProcessingRules $false

Organization-wide filters to Exchange transport rules¶

Gmail admin filters that apply to all users map to Exchange transport rules (mail flow rules).

# Example: Create an Exchange transport rule
New-TransportRule -Name "External Email Disclaimer" `
    -FromScope "NotInOrganization" `
    -ApplyHtmlDisclaimerText "<p>This email originated from outside the organization.</p>" `
    -ApplyHtmlDisclaimerLocation "Prepend"

Delegation and shared mailbox migration¶

Gmail delegation types¶

Configure delegation in Exchange Online¶

# Grant full access to a shared mailbox
Add-MailboxPermission -Identity "shared@contoso.com" `
    -User "user@contoso.com" `
    -AccessRights FullAccess `
    -InheritanceType All

# Grant send-as permission
Add-RecipientPermission -Identity "shared@contoso.com" `
    -Trustee "user@contoso.com" `
    -AccessRights SendAs

# Grant send on behalf
Set-Mailbox -Identity "shared@contoso.com" `
    -GrantSendOnBehalfTo "user@contoso.com"

Creating and running migration batches¶

Step 1: Prepare the CSV file¶

Create a CSV file with the mapping of Google Workspace mailboxes to Exchange Online mailboxes:

EmailAddress
user1@contoso.com
user2@contoso.com
user3@contoso.com

Step 2: Create the migration batch¶

In Exchange Admin Center:

1. Navigate to Migration.
2. Click Add migration batch.
3. Select Migration to Exchange Online.
4. Select Google Workspace migration.
5. Select the migration endpoint created earlier.
6. Upload the CSV file.
7. Configure start and completion options:
   • Start automatically or Start manually.
   • Complete automatically or Complete manually (recommended: complete manually after validation).

# Alternative: Create migration batch via PowerShell
New-MigrationBatch -Name "Batch1-IT-Department" `
    -SourceEndpoint "GoogleWorkspaceEndpoint" `
    -CSVData ([System.IO.File]::ReadAllBytes("C:\migration\batch1.csv")) `
    -TargetDeliveryDomain "contoso.mail.onmicrosoft.com" `
    -AutoStart

Step 3: Monitor migration progress¶

# Check migration batch status
Get-MigrationBatch -Identity "Batch1-IT-Department" |
    Format-List Status, TotalCount, SyncedCount, FailedCount

# Check individual user migration status
Get-MigrationUser -BatchId "Batch1-IT-Department" |
    Format-Table Identity, Status, ItemsSynced, ItemsSkipped -AutoSize

# Check for errors
Get-MigrationUser -BatchId "Batch1-IT-Department" -Status Failed |
    Format-List Identity, Error

Step 4: Complete the migration batch¶

After validating that all items have synced:

# Complete the migration batch (finalizes the migration)
Complete-MigrationBatch -Identity "Batch1-IT-Department"

Until the migration batch is completed, the migration tool performs incremental sync every 24 hours. New emails arriving in Gmail will sync to Exchange Online. Do not complete the batch until you are ready for DNS cutover. Completing the batch stops incremental sync.

DNS cutover: MX record migration¶

Pre-cutover preparation¶

1. Reduce MX record TTL to 300 seconds (5 minutes) at least 48 hours before cutover.
2. Communicate cutover window to all users.
3. Verify all migration batches show "Synced" status.
4. Test mail flow by sending test messages to the Exchange Online mailbox directly (bypass DNS).

MX record change¶

Replace Google MX records with Microsoft 365 MX records:

Additional DNS records¶

Post-cutover validation¶

# Verify MX record propagation
Resolve-DnsName -Name contoso.com -Type MX

# Verify SPF record
Resolve-DnsName -Name contoso.com -Type TXT

# Verify mail flow by sending test emails
# Internal to internal
# External to internal
# Internal to external

Post-migration tasks¶

Verify migration completeness¶

# Check item counts match between Gmail and Exchange
Get-MailboxStatistics -Identity user@contoso.com |
    Format-List ItemCount, TotalItemSize

# Compare with Gmail mailbox size (Google Admin Console > Users > user)

Configure Outlook clients¶

• Deploy Outlook desktop via Intune or Microsoft 365 Apps deployment.
• Configure Outlook profiles (auto-discovered via DNS autodiscover record).
• Deploy Outlook mobile app via Intune MAM policies.
• Train users on Outlook features: Focused Inbox, @mentions, My Day calendar view.

Clean up Google Workspace¶

1. Wait 30 days after cutover before decommissioning Google Workspace.
2. Export any remaining data via Google Takeout (admin export).
3. Disable Gmail in Google Workspace Admin Console (keeps accounts for Drive migration if still in progress).
4. Cancel Google Workspace licenses after all workloads are migrated.

Troubleshooting common issues¶

Capacity planning¶

Duration depends on average mailbox size. Assume 2-10 GB/mailbox/day throughput for Google Workspace migration in EAC.