Relay

Allows an SMTP server to accept any email destined for other hosts and re-deliver that mail to the proper host, much like a feild and track relay race where the SMTP servers are the the runners and the email message is the baton.

To retransmit a received message from one station to another station. 2. An electromechanical or semiconductor switch (i.e., solid-state relay) in which a current or voltage applied across one port or terminal controls electrical currents or voltages that appear across another terminal or terminals.