Email Migration is not accessible if you prefer old ways to migrate. Legacy migration methods involve risk, and there is also no guarantee whether your complete mailbox transfer or not. For example, the Cutover migration this method consists of "all or nothing," which means you only complete mailbox or noting will be migrated.
Sometimes professionals are also stuck in these methods. So what do you do as a beginner? Well, shoviv suggests avoiding these manual tactics and using an ultimate migrator for Office 365 or Exchange mailbox.
An Ultimate Migrator for Office 365 Mailbox