Commercial mail for outlying business centre (7,4)
I believe the answer is:
trading post
'outlying business centre' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'commercial mail' is the wordplay.
'commercial' becomes 'trading' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'mail' becomes 'post' (synonyms).
'trading'+'post'='TRADING POST'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for trading post that I've seen before include "store in a remote area" , "Store in a remote place" , "general store" , "Remote supplier" .)