Message this writer sent back with trouble (5)
I believe the answer is:
'message' is the definition.
(email is a type of message)
'this writer sent back with trouble' is the wordplay.
'this writer' becomes 'me' (the person who wrote the clues).
'sent back' shows that the letters should be reversed in order.
'with' is a charade indicator (letters next to each other).
'trouble' becomes 'ail' (synonyms).
'me' backwards is 'em'.
'em'+'ail'='EMAIL'
(Other definitions for email that I've seen before include "Send one online" , "Post" , "Messages between computer terminals" , "Messages via the internet" , "Internet-borne communication" .)