Crossword Genius

It describes letters to pals perhaps (6)

Ross

I believe the answer is:

postal

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'it describes letters' is the definition.
The definition suggests a singular noun but the answer is not.

'to pals perhaps' is the wordplay.
'perhaps' indicates an anagram.
'to'+'pals'='topals'
'topals' is an anagram of 'POSTAL'.

Can you help me to learn more?

(Other definitions for postal that I've seen before include "Relating to mail service" , "Type of order" , "to go so mad in America" , "Relating to mail delivery" , "To do with snail mail" .)

I've seen this clue in The Globe and Mail.
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