I have recently migrated an on-premises Exchange 2010 environment to Exchange 2016. The old 2010 environment included a server strictly used for client access and hub transport, it contains no mailboxes. However, there are a few remaining mailboxes in the 2010 environment that receive messages.
The issue I am seeing is the 2016 server is relaying messages through the CAS/HT server to the MB/CAS/HT server. Is it safe to simply uninstall the CAS/HT only server so that messages go directly to the MB/CAS/HT? All incoming and outgoing messages flow through the new 2016 server.