A CFMachPort object is a wrapper for a native Mach port (
mach_port_t). Mach ports are the native communication channel for the macOS kernel.
CFMachPort does not provide a function to send messages, so you primarily use a CFMachPort object if you need to listen to a Mach port that you obtained by other means. You can get a callback when a message arrives on the port or when the port becomes invalid, such as when the native port dies.
To send data, you must use the Mach APIs with the native Mach port, which is not described here. Alternatively, you can use a CFMessagePort object, which can send arbitrary data.
Mach ports only support communication on the local machine. For network communication, you have to use a CFSocket object.