Mail being sent to distant branch (7)
I believe the answer is:
outpost
'branch' is the definition.
(I have seen 'Remote branch' mean 'outpost' so perhaps 'branch' could also mean 'outpost')
'mail being sent to distant' is the wordplay.
I cannot really understand how this works, but
'mail' could be 'post' (synonyms) and 'post' is present in the answer.
The remaining letters 'out' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for outpost that I've seen before include "Remote stronghold" , "Remote branch" , "Small group of soldiers" , "settlement difficult to reach?" , "Remote part of an empire" .)