Mail text of play supplying added note

I believe the answer is:

postscript

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'note' is the definition.
(postscript is a kind of note)

'mail text' is the wordplay.
'mail' becomes 'post' (I've seen this before).
'text' becomes 'script' (I've seen this before).
'post'+'script'='POSTSCRIPT'

'of play supplying added' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for postscript that I've seen before include "part of letter" , "Addition to a letter" , "Extra lines" , "PS" , "Last added words" .)

I've seen this clue in The Telegraph.

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