Clue: Mail a newspaperman returned, at first showing indifference (8)
Answer: DEADNESS
Explanation: Definition: indifference
 **Reversal of**(… returned) [ SEND(to mail/to forward to) + A + ED(abbrev. for "editor", a newspaperman/one of the newspaper staff) ] ***plus***(at) ***1st letter of***(first) "showing".
Defn: …/unresponsiveness.