React to internal correspondence (7)

I believe the answer is:

respond

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'react' is the definition.
(I know that respond is a kind of react)

'internal correspondence' is the wordplay.
'RESPOND' is hidden within the letters.
However, I am not sure how this is indicated.

'to' acts as a link.

Can you help me to learn more?

(Other definitions for respond that I've seen before include "Write back" , "Answer or react" , "Reply - react" , "React (positively) to a stimulus or treatment" , "Come back" .)

I've seen this clue in The Irish Times.

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