SFO posting (3)
I believe the answer is:
eta
'sfo posting' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eta that I've seen before include "Basque separatist movement" , "Militant Basque organisation - Greek letter" , "when it might reach us?" , "Foreign letter" , "European separatists, initially" .)