> Also, you can't overlook that a significant number of people use Gmail/Google Apps and Outlook.com/Office 365 which each use a proprietary communication proto

> Also, you can't overlook that a significant number of people use Gmail/Google Apps and Outlook.com/Office 365 which each use a proprietary communication protocol that is unlikely to change in the future. All of those support IMAP currently, an open standard. Exchange has MAPI as well. Email is the best federated system we might ever have, and it has thousands of clients that can work with nearly any provider. JMAP has not taken off, but there is a chicken and egg problem. Most clients don't support it so there is no pressure on services to support it. Though I imagine if Gmail supported it then suddenly all the clients would support it