I posted letters to bank (7)
I believe the answer is:
deposit
'bank' is the definition.
(I've seen this before)
'i posted letters' is the wordplay.
'letters' is an anagram indicator.
'i'+'posted'='iposted'
'iposted' anagrammed gives 'DEPOSIT'.
'to' is the link.
(Other definitions for deposit that I've seen before include "Put down - initial payment" , "Money up front" , "Part payment on a purchase" , "Sediment or bank lodgment" , "First instalment" .)