Whizz around circulating mail for herald (8)
I believe the answer is:
proclaim
'for herald' is the definition.
(I've seen this in another clue)
'whizz around circulating mail' is the wordplay.
'whizz' becomes 'pro' (both can mean someone skilled at something).
'around' becomes 'c' (abbreviation for 'circa').
'circulating' indicates anagramming the letters.
'mail' anagrammed gives 'laim'.
'pro'+'c'+'laim'='PROCLAIM'
(Other definitions for proclaim that I've seen before include "Speak out" , "Declare formally" , "shout from the housetops" , "Announce officially or declare publicly" , "Reveal" .)