Your users can import their own email, contacts, and other mailbox information to an Office 365 mailbox created for them. Your organisation also can work with a partner to migrate email.
Before you start an email migration, review limits and best practices for Exchange Online to make sure you get the performance and behaviour you expect after migration.
See Decide on a migration path or Exchange migration advisors for help with choosing the best option for your organisationYour users can import their own email, contacts, and other mailbox information to an Office 365 mailbox created for them. Your organisation also can work with a partner to migrate email.