Unwanted messages about upcoming maps (4)
I believe the answer is:
spam
'unwanted messages' is the definition.
(spam emails)
'upcoming maps' is the wordplay.
'upcoming' says the letters should be written backwards (in a down clue coming up is backwards).
'maps' written backwards gives 'SPAM'.
'about' acts as a link.
(Other definitions for spam that I've seen before include "Possible item from menu" , "Computer junk mail" , "Unwanted e-mails" , "(Send) junk mail" , "Unwelcome approach" .)