Message from girl I am excited about (5)
I believe the answer is:
'message' is the definition.
(email is a type of message)
'from girl i am excited about' is the wordplay.
'from' says the answer is hidden in the clue.
'about' says the letters should be written backwards.
'liame' is hidden in the letters of 'girl i am excited'.
'liame' back-to-front is 'EMAIL'.
(Other definitions for email that I've seen before include "Digital message" , "Messages via the internet" , "Internet-borne communication" , "Message sent via computer" , "Messages between computer terminals" .)