Use the data migration service
Supported editions for this feature: Business Starter, Standard, and Plus; Enterprise; Education Fundamentals, Standard, Teaching and Learning Upgrade, and Plus; Nonprofits; G Suite Basic and Business; Essentials. Compare your edition
If you have Essentials edition, you can migrate only calendar data and contacts. You can't migrate email.
You can use the data migration service to easily migrate your users' mail, contacts, and calendars to Google Workspace. You set it up and control everything right in the Google Admin console. There’s no need to install a client or application. Setup is simplified, and most mail server connections can be made automatically.