Endless junk mail for health resort (3)
I believe the answer is:
spa
'health resort' is the definition.
(spa can mean a health resort)
'endless junk mail' is the wordplay.
'endless' means to remove the last letter.
'junk mail' becomes 'spam' (I've seen this before).
'spam' with its last letter removed is 'SPA'.
'for' acts as a link.
(Other definitions for spa that I've seen before include "Watering place" , "place of treatment" , "Mineral-water resort" , "where health benefits are offered" , "Water-cure town" .)