I have performed a number of successful migrations between O365 and on-premise Exchange servers. I can consult, plan, and implement any such migration, so long as the Exchange level is 2007 or newer. I have performed these migrations manually with my own scripting, with 3rd party toolkits, and also with the new microsoft wizards. I can provide a reasonable guarantee of success without loss of mailflow. I can cope with situations that are officially unsupported by Microsoft using my own scripting or by performing an intermediate migration.