Outlook 2016 cached mode global address book not updating
The mailbox databases are currently active on E15MB2.
With no load balancer available to me at this stage I am using DNS round robin, which is not as good as proper load balancing but will do the job for now.
In Exchange 2010 high availability for the Client Access server was achieved through the configuration of a CAS Array and some form of load balancing (hardware/virtual, or Windows NLB).
Although the CAS Array no longer exists in Exchange 2013, and other architectural changes mean that load balancing can be approached in different ways, the basic concept of a single namespace for Outlook connectivity remains.
Eventually Outlook may autodiscover other available Client Access servers in the site and connect to one of them, but it is not an ideal user experience.
To improve this situation we need to look at the Outlook Anywhere configuration for the Client Access servers.