Commission post office in unusually inapt surroundings (7)

I believe the answer is:

appoint

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'commission' is the definition.
(thesaurus)

'post office in unusually inapt surroundings' is the wordplay.
'post office' becomes 'po' (abbreviation).
'unusually inapt' becomes 'apt' (I can't justify this - if you can you should give a lot more credence to this answer).
'surroundings' is an insertion indicator.
'po'+'in'='poin'
'poin' inserted within 'apt' is 'APPOINT'.

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(Other definitions for appoint that I've seen before include "Establish" , "Fix" , "Settle" , "Give job to" , "Put into a post" .)

I've seen this clue in The Irish Independent.

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