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.
PST-based migrations are not documented as they are merely a file export/import procedure, which requires little preparation. You may want to document a procedure that states where the PST files are stored and how they are named, and even list the PST file passwords if password protection is required.
In order for Exchange Online to access your IMAP server/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 the existing IMAP mailboxes in CSV format which is imported into the Exchange Online Control Panel...