The implementation of Exchange Online, part of Microsoft's Office365 cloud offering, provides: greater reliability, increased performance, additional features, and allows for continued improvement with e-mail.
None. There will be no disruption to the flow of email and no email will be lost. Synchronization to a mobile device should not need re-configuration. Devices should update automatically after the migration. Current versions of Microsoft Office are not impacted. Exchange Online fully supports clients for Outlook 2010/13/16 and Outlook for Mac 2011/2016.