Word with mail or box (5)
I believe the answer is:
voice
'word with mail or box' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for voice that I've seen before include "Sound produced in speaking" , "Sound produced by humans" , "Sound produced in the larynx" , "Utter - part" , "(Human) utterance" .)