Before beginning the migration process, it is important to ensure that your environment has been prepared and that all requirements have been met.
Due to the varying requirements and processes we have broken these down between types of migrations.
In order for Exchange Online to access your IMAP sever/service, it must be accessible via the IMAP protocol from the Internet, which is generally the case.
It is important that the users be created via the Office 365 administrative interface either individually or in bulk.
You also need to prepare a listing of existing IMAP mailboxes in CSV format which is imported into the Exchange Online control panel. This CSV maps the IMAP credentials (e-mail address, username, and password) to the Exchange Online mailbox.