Microsoft announced in circa May 2015 that Outlook.com users would undergo a migration of the backend servers to the same system supporting Office365, and with certain enhancements as a consequence. See:
https://blogs.office.com/2015/05/21/new-ways-to-get-more-done-in-outlook-com/
The Migration is stated in the above link as "opt-in". I for one have heard nothing at all about this migration, in particular the procedure to "opt-in".
Does anybody know anything?