Revealed son carrying mail for distant territories (8)
I believe the answer is:
outposts
'distant territories' is the definition.
(I've seen this before)
'revealed son carrying mail' is the wordplay.
'revealed' becomes 'out' (as in news which is out).
'son' becomes 's' (genealogical abbreviation for son).
'carrying' says to put letters next to each other (in a down clue, the bottom letters carry others).
'mail' becomes 'post' (synonyms).
's' put after 'post' is 'posts'.
'out'+'posts'='OUTPOSTS'
'for' is the link.
(Other definitions for outposts that I've seen before include "distant territories" , "Remote settlements" , "Military stations in the wilds" , "Distant military camps" .)