Again I send in by return (7)
I believe the answer is:
riposte
'return' is the definition.
('riposte' can be a synonym of 'return')
'again i send in' is the wordplay.
'again' becomes 're'.
'send' becomes 'post' ('post' can be a synonym of 'send'**).
'in' is an insertion indicator.
'i'+'post'='ipost'
're' going around 'ipost' is 'RIPOSTE'.
'by' is the link.
(Other definitions for riposte that I've seen before include "Fencer's counterattack" , "Return thrust or repartee" , "Quick sharp reply" , "Poster I alter for repartee" , "Quick answer" .)