A position, that is, for a delivery man (6)

I believe the answer is:

postie

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'a delivery man' is the definition.
The definition suggests a singular noun which matches the answer.

'a position that is' is the wordplay.
'a position' becomes 'post' (synonyms).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'post'+'ie'='POSTIE'

'for' acts as a link.

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(Another definition for postie that I've seen is " Mail deliverer (informal)".)

I've seen this clue in the Evening Standard.

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