Analogous to a letter writer (13)
I believe the answer is:
correspondent
I believe this clue is a double definition.
'analogous' is the first definition.
(synonyms)
'a letter writer' is the second definition.
('correspondent' can be a synonym of 'letter writer')
'to' is the link.
(Other definitions for correspondent that I've seen before include "Person sending letters or written reports - agreeing" , "Reporter on special subject or from overseas" , "Newspaper writer" , "Pen-friend" , "Journalist; letter-writer" .)