Electronic communication has upset me - trouble follows (1-4)
'electronic communication' is the definition.
(I've seen this before)
'upset me trouble follows' is the wordplay.
'upset' says the letters should be written backwards.
'trouble' becomes 'ail' (synonyms).
'follows' is a charade indicator (letters next to each other).
'me' in reverse letter order is 'em'.
'has' is the link.
(Other definitions for e-mail that I've seen before include "Online post", "Digital message", "Messages via the internet", "Messages between computer terminals", "Electronic post".)