Cash Dept mishandled mail (8)
I believe the answer is:
despatch
'mail' is the definition.
(both can mean to send)
'cash dept mishandled' is the wordplay.
'mishandled' indicates an anagram.
'cash'+'dept'='cashdept'
'cashdept' is an anagram of 'DESPATCH'.
(Other definitions for despatch that I've seen before include "expedition" , "Send off, kill" , "Send out - chest pad (anag)" , "Bulletin" , "Give send-off" .)