Move a mailbox
Keeps folders, read marks and original dates. The source is opened read-only, always, and you can run it as many times as you need — dry run, bulk pass, final pass on cutover day — because anything already copied is skipped, never duplicated.
What happens to the passwords
They are encrypted while the job needs them and deleted the moment it ends — they are never stored afterwards and never written to logs. Even so: if you can, use an app password or a temporary one.