Cease sending post (4)
I believe the answer is:
stop
'cease' is the definition.
(I know that cease can be written as stop)
'sending post' is the wordplay.
'sending' is an anagram indicator (letters are sent to different positions).
'post' with letters rearranged gives 'STOP'.
(Other definitions for stop that I've seen before include "Plug; cease" , "Come to a halt" , "Organ knob; get bus here" , "Blockage" , "Cease; organ voice" .)