RDS Email Discovery: Subscribe to Your RemoteApp Feed
Let users subscribe to your RDS web feed with just their email address: add a public _msradc TXT record that points to the RDWeb webfeed.aspx URL.
Autodiscover Ignores Exchange Online? Check the Registry
Outlook asks for Office 365 credentials while the mailbox is still on Exchange on-premises: set ExcludeExplicitO365Endpoint under the Autodiscover key.