You might get a response from the enterprise mailing list, but seriously I doubt it. Once such a migration was complete the enterprise would unsubscribe from the list. My understanding is that o365 lacks just about any form of import features, as Thunderbird lacks export features you might find this requires multiple levels of conversion. With mail needing to be exported as EML files and contacts as CSV files. I find it interesting you say they have outgrown Thunderbird, what exactly does using outlook offer that Thunderbird does not to justify the expense and time? Mostly when I hear that it is the Consultant admitting all they know is Microsoft.