Google Workspace Migration

Recommended Concurrent Settings for Google Workspace to Microsoft 365 Mailbox Migration

Amos Gikunda Sep 29, 2026 868 views

Question details

The user wants to know the optimal values for Maximum Concurrent and Maximum Concurrent Incremental settings when migrating a batch of mailboxes from Google Workspace to Microsoft 365.

Recommended Concurrent Settings for Google Workspace Mailbox Migration

Product: Microsoft Exchange Online
Device & OS: not provided
Scenario: Configuring a migration batch to transfer multiple users (e.g., 240 mailboxes) from Google Workspace to Microsoft 365 without triggering API limits.
Observed behavior: Seeking the best configuration parameters to maximize migration efficiency and prevent source-service throttling.

Before you start

Before adjusting concurrency limits, ensure you have Exchange administrator permissions in Microsoft 365 and review Google Workspace's API quota limits to understand your baseline capacity.

Solution 1Recommended

Start with Default Concurrency Limits and Scale Gradually

The most reliable approach is to begin with the default migration settings, monitor for throttling, and only increase the limits if the source service handles the load well.

Microsoft sets default values at 20 for Maximum Concurrent migrations and 10 for Maximum Concurrent Incremental synchronizations. It is highly advised not to set these values to match your total user count (e.g., 240). Migrating all mailboxes simultaneously often overwhelms the source service API, leading to throttling, stalled migrations, and increased overall completion times.

Set initial default values

When creating your migration batch in the Exchange admin center, leave the Maximum Concurrent value at 20 and Maximum Concurrent Incremental at 10.

Monitor batch performance

Start the migration batch and observe the status. Check the migration logs for 'StalledDueToSource' messages or API throttling warnings.

Gradually increase limits

If the migration proceeds smoothly, edit the batch settings to gradually increase the Maximum Concurrent value in small increments (up to a theoretical maximum of 100), depending on what your Google Workspace limits allow.

Start with Default Concurrency Limits and Scale Gradually

Best Practice: Migrating all users at exactly the same time is usually unnecessary. Using a staggered, default-driven approach ensures a much higher success rate without manual intervention for stalled batches.

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Frequently Asked Questions

What happens if I set the Maximum Concurrent migrations equal to my total user count?

Setting the concurrent value too high usually causes the source service (Google Workspace) to rate-limit or throttle the connection. This results in stalled migration batches, timeouts, and significantly slows down the entire migration process.

What is the absolute maximum value I can set for concurrent migrations in Exchange Online?

The maximum allowed value you can configure for concurrent migrations is typically 100. However, achieving this speed successfully depends entirely on your network infrastructure and the API rate limits imposed by the source environment.

What is the difference between Maximum Concurrent and Maximum Concurrent Incremental?

Maximum Concurrent refers to the maximum number of mailboxes undergoing their initial, full synchronization at the same time. Maximum Concurrent Incremental refers to the number of mailboxes concurrently performing delta syncs to pull in new emails that arrived after the initial sync.

Migration & Recovery