Why Winlink is an email-over-radio system where stations on the air connect to an RMS (Remote/Radio Message Server) that relays their traffic to and from the internet email system. Because it bridges two different networks, RF and the internet, it is called a gateway. Users connect to a gateway with Winlink Express over VHF/UHF packet or HF modes such as VARA or Pactor.
Watch out A Terminal Node Controller is just the modem hardware that turns data into packet tones at an individual station; it does not provide the internet link. RJ-45 is the 8-pin connector used for Ethernet cabling.
RMS bridges radio to internet email, and a bridge between networks is a gateway.