Trouble following space communication (5)
I believe the answer is:
'communication' is the definition.
(email is a kind of communication)
'trouble following space' is the wordplay.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble').
'following' is a charade indicator (letters next to each other).
'space' becomes 'em' (in typography, a space as wide as a letter 'm').
'ail' after 'em' is 'EMAIL'.
(Other definitions for email that I've seen before include "Spam perhaps" , "Send one online" , "Message sent via computer" , "Electronic communication" , "Electronic message" .)