Poster sent at fast rate (6)
I believe the answer is:
presto
'fast rate' is the definition.
'presto' can be an answer for 'fast' (musical instruction). I am unsure of the 'rate' bit.
'poster sent' is the wordplay.
'sent' indicates anagramming the letters (send can mean to excite or stimulate).
'poster' with letters rearranged gives 'PRESTO'.
'at' is the link.
Can you help me to learn more?
(Other definitions for presto that I've seen before include "Moving quickly" , "rapidly" , "In a quick tempo (music)" , "Hey . . . . ., says the magician (6)" , "29 [ADAGIO]? On the contrary" .)