Padded envelope (6)
I believe the answer is:
mailer
'padded envelope' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mailer that I've seen before include "writer from America" , "novelist" , "Poster" , "American author of The Naked and the Dead, d. 2007" , "person at the post?" .)