In a scaled-out, multi-tenant broker environment, the host on which the container is running is often different from the host to which a client is establishing the tcp connection. The 'hostname' field in the connection open performative was added to support this scenario. Currently there's no way to control this from the Messenger API.
(1) (preferred) add a new 'networkhost' field to Message to allow the network address to be specified. If provided, this information would be used when establishing the network connection and the data in the 'address' field would be used in the connection open hostname field. This is somewhat in line with the way that connection redirect (amqp:connection:redirect) is specified.
(2) extend the syntax of address with query string to supply hostname, e.g., username:password@tcpaddress:tcpport/entityname?hostname=foo where 'foo' would become the hostname used in the connection open frame. This is the approach used by the current Qpid AMQP 1.0 JMS client.