Mail worker no longer in theatre (4-9)

I believe the answer is:

post-operative

'no longer in theatre' is the definition.
(no longer in an operating theatre)

'mail worker' is the wordplay.
'mail' becomes 'post' (I've seen this before).
'worker' becomes 'operative' (I've seen this before).
'post'+'operative'='POST-OPERATIVE'

I've seen this clue in The Times.

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