Cease sending post (4)
I believe the answer is:
stop
'cease' is the definition.
(synonyms)
'sending post' is the wordplay.
'sending' is an anagram indicator (letters are sent to different positions).
'post' is an anagram of '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" .)