Name him by return of post (4)
I believe the answer is:
liam
'name him' is the definition.
'Liam' can be an answer for 'him'. I am not certain of the 'name' bit.
'return of post' is the wordplay.
'return of' says the letters should be written in reverse.
'post' becomes 'mail' (synonyms).
'mail' backwards is 'LIAM'.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for liam that I've seen before include "Irishman" , "-- Neeson (actor)" , "Boy" .)