Brute has article to mail off (6)
I believe the answer is:
animal
'brute' is the definition.
(I know that animal is a type of brute)
'article to mail off' is the wordplay.
'article' becomes 'an' (English indefinite article).
'off' is an anagram indicator.
'mail' anagrammed gives 'imal'.
'an'+'imal'='ANIMAL'
'has' acts as a link.
(Other definitions for animal that I've seen before include "Any organism capable of voluntary movement" , "Brutal, sensual" , "It shares the world with vegetable and mineral" , "One sharing our kingdom" , "cat, perhaps" .)