Said to be a man of letters (4)
I believe the answer is:
'letters' is the definition.
(I've seen this before)
'said to be a man' is the wordplay.
'said to be' indicates a 'sounds like' (homophone) clue.
'a man' becomes 'male'.
'male' sounds like 'MAIL'.
'of' is the link.
(Other definitions for mail that I've seen before include "letter?" , "Flexible armour" , "Paper" , "Post in America" , "Letters - armour" .)