Coming soon to Android and Windows Mobile.
But you’ll have to add an Office 365 commercial account or on-premises Exchange 2016 mailbox to be able to use it.
This feature is well-known in Outlook desktop clients; and it’s always worked regardless of whether your mailbox is on Office 365 or Exchange on-premises.
On a somewhat related note, Microsoft finally completed the move from AWS to the Microsoft Cloud for the back-end infrastructure supporting this app. That goes a long way to easing many corporate security concerns.