On the Exchange Team Blog information on the new Exchange Server 2016 architecture has been published. One of the biggest changes is probably the elimination of the client access role. This means that there is now only one role, making deployment fairly simple. The Client Access role has now also been integrated into the Mailbox role. It is interesting to note that Microsoft is performing a role reversal here, as Exchange 2003 already had only one role that provided all functions. With Exchange 2007, the roles were then separated, initially into Hub Transport, Client Access and Mailbox. This concept was also retained in Exchange 2010. Consolidation began again with Exchange 2013, with only the Mailbox and Client Access roles. With Exchange 2016, we once again have just one system that performs all functions.
The DAG concept has been retained but improved. According to the Exchange Team Blog, the database failover time has been reduced by 33%. A load balancer is still used for high availability. As with Exchange 2013, the requirements for the load balancer are low.
The new standard protocol is now MAPI/HTTP, which was introduced with Exchange 2013 SP1. There will be no support for MAPI/CDO. Old applications that use the CDO must therefore be converted to EWS.
Apparently, the migration from Exchange 2013 to Exchange 2016 is also supported directly from the release, even a mixed operation of Exchange 2013 and Exchange 2016 should be possible.
So the tension is rising 
