Amour-clad protracted letters (5-4)

I believe the answer is:

chain-mail

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'amour-clad' is the definition.
I can't judge whether this defines the answer.

'protracted letters' is the wordplay.
'protracted' becomes 'chain' (I can't explain this - if you can you should believe this answer much more).
'letters' becomes 'mail' (I've seen this before).
'chain'+'mail'='CHAIN-MAIL'

Can you help me to learn more?

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

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