Cutover migration moves all mailboxes and data from an older Exchange server to either a newer on-premise Exchange server or to a cloud-based service.
The cutover migration process starts with the destination Exchange server -- on-premise or online -- which receives information about the mailboxes, groups, calendars, and contacts. The system then provisions the new mailboxes and copies content, duplicating as much of the original system as possible.
Administrators receive reports of the Cutover Migration including details of failed mailbox migrations. Old mail is deleted and the Exchange administrator can send mail directly to the new server and delete the cutover migration batch. At this point, the old Exchange server can be decommissioned.
IT administrators typically perform cutover migrations through the migration dashboard in the Administration Center or the Exchange Management Shell.
The migration process is limited to Exchange deployments of 1,000 mailboxes and can take numerous hours to days depending on the number of mailboxes and the volume of migrated content.
When migration involves a larger number of mailboxes or the process must be performed incrementally using smaller mailbox groups, administrators can opt for staged (partial) migration. Non-Exchange mailboxes can be migrated into a new Exchange server environment using Internet Message Access Protocol migration.
