It's possible to make a send-only teleporter, which will not receive items when fueled:
1. Build and fuel the teleporter.
2. Teleport something to it. This reveals the receive slot.
3. Take out the teleported item and put some other junk in the receive slot.
But this is clumsy. Instead the teleporter configuration should have a switch for send-only operation.

Turns out I was incorrect: it's possible for a teleporter with a full receive slot to receive more teleported stuff, which is then dumped on the ground next to the teleporter.