Post Office receives steamy image (5)
I believe the answer is:
photo
'image' is the definition.
(I know that photo is a type of image)
'post office receives steamy' is the wordplay.
'post office' becomes 'po' (abbreviation).
'receives' indicates putting letters inside (inserted letters are received).
'steamy' becomes 'hot' (both can mean erotic).
'po' enclosing 'hot' is 'PHOTO'.
(Other definitions for photo that I've seen before include "In brief, a snapshot" , "Snap, exposure, in short" , "Snap, pic" , "Snap (abbrev.)" , "This race finish is very close" .)