Very warm in the post office? Snap out of it! (5)

I believe the answer is:

photo

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'snap out of it' is the definition.
I can't tell whether this definition defines the answer.

'very warm in the post office?' is the wordplay.
'very warm' becomes 'hot' (I've seen this before).
'in the' means one lot of letters goes inside another.
'post office?' becomes 'po' (abbreviation).
'hot' inserted within 'po' is 'PHOTO'.

Can you help me to learn more?

(Other definitions for photo that I've seen before include "Snap - shot" , "Still" , "Snap, pic" , "Picture, in short" , "Snap (abbrev.)" .)

I've seen this clue in The Irish Independent.

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