Mail manager’s notice binding staff (10)
I believe the answer is:
postmaster
'mail manager's' is the definition.
(a postmaster manages post or mail)
'notice binding staff' is the wordplay.
'notice' becomes 'poster' (synonyms).
'binding' indicates putting letters inside.
'staff' becomes 'mast'.
'poster' placed around 'mast' is 'POSTMASTER'.
(Other definitions for postmaster that I've seen before include "who runs a local office?" , "Mail chief" .)