A discussion on the security stackexchange https://security.stackexchange.com/a/145674/37973 has raised the question of unidirectional transmission over Ethernet with the return path physically removed. Unidirectional reception with the transmitting wires unconnected certainly is possible, e.g. in simple Ethernet wiretapping tools like https://greatscottgadgets.com/throwingstar/
Would transmitting raw Ethernet frames be possible in this manner?
An answer to an earlier question (Ethernet Frames on Unidirectional Link) states that a response link is required for Ethernet autonegotiation, however older standards such as 10BASE-T should work (with a proper crossover cable) even in absence of autonegotiation. It's clear that the sender can't know if the message was received, but that can be handled in various ways, the question is if standard Ethernet network cards will send the required data over the physical layer in absence of any response/negotiation/handshake/etc.