Load Balancing in Exchange 2016

Like Exchange 2013, Exchange 2016 does not require session affinity at the load balancing layer.

To understand this statement better, and see how this impacts your designs, we need to look at how MBX2016 functions. From a protocol perspective, the following will happen:

1. A client resolves the namespace to a load balanced virtual IP address.
2. The load balancer assigns the session to a MBX server in the load balanced pool.
3. The Client Access services located on the MBX server authenticates the request and performs a service discovery by accessing Active Directory to retrieve the following information:The Client Access services located on the MBX server makes a decision on whether to proxy the request or redirect the request to another MBX infrastructure (within the same forest).
   1. Mailbox version (for this discussion, we will assume an Exchange 2016 mailbox)
   2. Mailbox location information (e.g., database information, ExternalURL values, etc.)
5. The Client Access services located on the MBX server queries an Active Manager instance that is responsible for the database to determine which Mailbox server is hosting the active copy.
6. The Client Access services located on the MBX server proxies the request to the Mailbox server hosting the active copy.

Read more at source: http://blogs.technet.com/b/exchange/archive/2015/10/08/load-balancing-in-exchange-2016.aspx