Throttling is entirely normal, so if you experience it, you shouldn't worry. Throttling is an essential security mechanism that ensures the service offered by your server remains healthy and responsive. It is called "throttling" because it limits the workload coming through the server. Without this, the server could become unresponsive or even crash completely, causing service interruptions for all users.

Tip: To minimize the impact on your migration process, please follow these guidelines:

When running your Microsoft 365 migration, you may get an error indicating the status code 429 Too Many Requests or 503 Service Unavailable.

These errors do not indicate that your migration has been stopped. They notify you that your tenant is under a lot of pressure and, therefore, cannot handle the required request.

You do not have to cancel your migration when you get these errors. You can wait since ShareGate Migrate will retry the procedure until the server can handle the requests required to proceed with the migration.

You can cancel the operation at any moment if you prefer to attempt the migration again later.

The goal of ShareGate Migrate is to complete your migration simply and efficiently, which means processing requests as fast as possible. Due to this, ShareGate Migrate can cause a heavy load on your tenant that contributes to throttling.

However, migration alone is not usually the only cause of throttling. The number of users on your tenant can also generate a significant load during business hours. Other reasons, such as backup applications running simultaneously to ShareGate Migrate, also contribute to the strain.

The best way to prevent throttling is to schedule significant migration procedures outside business hours (overnight or weekends are ideal).

If you are dealing with a business that runs across different time zones (thus eliminating the opportunity to run the migration with a low server load), review the applications that use your tenant to run. Limiting background application activity during the migration procedure reduces the chance of throttling.

If neither of those options is possible, it may be best to split a large migration into smaller intervals. Migrate a bit at a time, and the request load on the server will be significantly less.

You can check out Microsoft's SharePoint Online and OneDrive Migration Speed article for information on the factors that affect migration speed and some best practices.

Throttling may cause frustration, but at the end of the day, it means that your Microsoft 365 tenant is being used to its full potential.

Experiencing some throttling is normal, but significant throttling indicates an issue. Significant throttling consists of more than 30% of requests being throttled for 30 minutes or more.

As an approved Microsoft partner and vendor, ShareGate Migrate follows best practices recommended by Microsoft to reduce throttling. These include the following: