Insult by sending cakes back (4)
I believe the answer is:
snub
'insult by sending' is the definition.
'snub' can be an answer for 'insult' (snub can mean to insult or humiliate). I am not sure about the 'by sending' bit.
'cakes back' is the wordplay.
'cakes' becomes 'buns' (cake is a type of bun).
'back' is a reversal indicator.
'buns' written backwards gives 'SNUB'.
Can you help me to learn more?
(Other definitions for snub that I've seen before include "Rudely ignore" , "Insult by ignoring" , "put down" , "Treat with disdain" , "Rebuff; brush-off" .)