Stop circulating mail (4)
I believe the answer is:
post
'mail' is the definition.
(I've seen this before)
'stop circulating' is the wordplay.
'circulating' is an anagram indicator.
'stop' is an anagram of 'POST'.
(Other definitions for post that I've seen before include "Job; upright timber" , "Publish' mail' job" , "Appointment (with the Royal Mail?)" , "type of support" , "Mail; wooden stake" .)