Correspondence made by accident? (11)
I believe the answer is:
coincidence
This clue is a double definition.
'correspondence' is the first definition.
(thesaurus)
'accident?' is the second definition.
(coincidence is a kind of accident)
'made by' acts as a link.
(Other definitions for coincidence that I've seen before include "pure chance" , "Chance event" , "Remarkable concurrence" , "Fluke" , "Simultaneous or connected occurrence" .)