A new stamp I designed, helping to identify unwanted mail (4-4)

I believe the answer is:

anti-spam

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

'designed helping to identify unwanted mail' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'a new stamp i' is the wordplay.
'a' becomes 'an'.
'new' indicates an anagram.
'stamp'+'i'='stampi'
'stampi' with letters rearranged gives 'tispam'.
'an'+'tispam'='ANTI-SPAM'

Can you help me to learn more?

I've seen this clue in The Hindu.

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