A network protocol unit interface is described that uses a message engine to transfer contents of received network protocol units in message segments to a destination message engine. The network protocol unit interface uses a message engine to receive messages whose content is to be transmitted in network protocol units. A message engine transmits message segments to a destination message engine without the message engine transmitter and receiver sharing memory space. In addition, the transmitter message engine can transmit message segments to a receiver message engine by use of a virtual address associated with the receiver message and a queue identifier, as opposed to a memory address.