Ventilate armour using adoring letters (3-4)

I believe the answer is:

fan-mail

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

'letters' is the definition.
(I've seen this before)

'ventilate armour using adoring' is the wordplay.
I cannot really understand how this works, but
'armour' could be 'mail' (mail is a kind of armour) and 'mail' is found in the answer.
The remaining letters 'fan' is a valid word which might be clued in a way I don't see.
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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