One sent by the landlord? (6)
I believe the answer is:
letter
'the landlord?' is the definition.
(landlords let property)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for letter that I've seen before include "Alphabetic character" , "reference?" , "Communication via the postman" , "Unit of alphabet" , "Written note" .)