Crossword Genius

Using mail appointment (7)

Ross

I believe the answer is:

posting

I'm a little stuck... Click here to teach me more about this clue!

'appointment' is the definition.
(thesaurus)

'using mail' is the wordplay.
I cannot really understand how this works, but
'mail' could be 'post' (synonyms) and 'post' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

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