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.Paul is a Microsoft MVP for Office Servers and Services.
Although a Database Availability Group can provide high availability for the databases hosted on the Mailbox servers, the Client Access server needs to be considered separately for HA.
Netstat shows me that the client has resolved mail.exchange2013to 192.168.0.188 and Outlook is connecting to E15MB2 at the moment.
netstat -ano | findstr ":80" TCP 192.168.0.1967 192.168.0.1 ESTABLISHED 2272 TCP 192.168.0.1968 192.168.0.1 ESTABLISHED 2272 TCP 192.168.0.1979 192.168.0.1 ESTABLISHED 2272 TCP 192.168.0.1980 192.168.0.1 ESTABLISHED 2272 So to test high availability I shut down E15MB2 while observing the Outlook connection status dialog.
You'll be able to tell it has taken effect when an Outlook autoconfiguration test returns the new value for Exchange HTTP.
After waiting a while and then restarting Outlook the client is connecting to the newly configured namespace.