The last part is on board with dispatches (5)
I believe the answer is:
sends
'dispatches' is the definition.
(I've seen this in another clue)
'the last part is on board' is the wordplay.
'the last part' becomes 'end' (I've seen this in another clue).
'is on' means one lot of letters goes inside another.
'board' becomes 'ss' (I've seen this in other clues).
'end' placed inside 'ss' is 'SENDS'.
'with' acts as a link.
(Other definitions for sends that I've seen before include "Transmits" , "Causes to go somewhere" , "Despatches" .)