How express letters are delivered? (9)
I believe the answer is:
posthaste
'how express' is the definition.
'posthaste' can be an answer for 'express' (I've seen this before). I am not sure about the 'how' bit.
'letters are delivered?' is the wordplay.
'letters' becomes 'post' (letters in the mail or post).
'are delivered?' becomes 'haste' (I am not sure about this - if you are sure you should believe this answer much more).
'post'+'haste'='POSTHASTE'
Can you help me to learn more?
(Other definitions for posthaste that I've seen before include "With particular speed" , "With great speed and urgency" , "Speedily" , "Yes!" , "at the double" .)