Carrier of a letter from a courtier (7)
I believe the answer is:
courier
'carrier' is the definition.
(thesaurus)
'a letter from a courtier' is the wordplay.
'a letter' becomes 't'.
'from' is a deletion indicator.
'courtier' with 't' taken away is 'COURIER'.
'of' is the link.
(Other definitions for courier that I've seen before include "Message-carrier" , "guide for tourists" , "Type" , "Messenger, runner" , "Delivery messenger" .)