As part of a Microsoft 365 or Office 365 deployment, you can migrate the contents of user mailboxes from a source email system to Microsoft 365 or Office 365. When you do this all at one time, it's called a cutover migration. Additionally, this migration method moves mail users, mail contacts, and mail-enabled groups with their membership. Choosing a Cutover Migration is suggested when:

Your current on-premises Exchange organization is Microsoft Exchange Server 2003 or later.

Your on-premises Exchange organization has fewer than 2,000 mailboxes.

Also, to know more about Cloud PC Services or migrating from Gmail to Office 365 visit O365CloudExperts.