Electronic message (1-4)
(Other definitions for e-mail that I've seen before include "Message sent via computer" , "Online correspondence" , "A lime (anag.)" , "Correspondence sent via internet" , "Web post" .)
'electronic message' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for email that I've seen before include "Spam perhaps" , "Electronic communication" , "Internet-borne communication" , "Message sent via computer" , "Send one online" .)