Passes on (a message) (6)
I believe the answer is:
relays
'passes on a message' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for relays that I've seen before include "Receives and passes on" , "Races featuring running teams and baton passing" , "Races where a baton is passed from one to another" , "Races with team members who pass a baton" , "Transmits" .)