Create a crossword mail-out from compost heap (7)

I believe the answer is:

compile

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'create a crossword mail-out' is the definition.
I can't tell whether this defines the answer.

'compost heap' is the wordplay.
'compost' becomes 'com' (I can't justify this - if you can you should believe this answer much more).
'heap' becomes 'pile' (synonyms).
'com'+'pile'='COMPILE'

'from' acts as a link.

Can you help me to learn more?

(Other definitions for compile that I've seen before include "Marshal" , "Put together" , "Assemble (a collection)" , "Polemic (anag.)" .)

I've seen this clue in the Sydney Morning Herald.

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