How does the Gmail unsubscribe button work?

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Sat May 30 2020 19:13:31 GMT+0000 (Coordinated Universal Time)

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List-Unsubscribe: 
  <mailto:test@example.com>, 
  <https://example.com/unsubscribe?uid=0000>
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https://blog.leavemealone.app/how-does-the-gmail-unsubscribe-button-work/