Are you now unsubscribed?

Question

Fight against spam

Comrades,
quite recently I marked a letter with a newsletter from one store as SPAM in the mailbox on mail.ru. I have ordered from them before.
Less than a day passes, and I receive a letter from them - You are now unsubscribed.
The question is how did they know about it? mail.ru somehow reports that a complaint has been received?
Thank you.

Answer 1

It is likely that Mail.ru, following Google, implemented this mechanism www.list-unsubscribe.com/ in case of clicking on the "Spam" button.