The unsubscribe link is how spammers know that the autogenerated email address they are sending to is read by a human being. It makes the address more valuable when sold to another spammer. That one spammer may stop sending you messages from the same brand, to avoid landing in blacklists, but his other brands and his affiliates will be sending you more.
The US is a bit different from the rest of the world since US law (the Yes-You-Can-Spam act) requires that US-based spammers include and respect an unsubscribe link. Neither requirement is actively enforced, so the question of whether one can expect an unsubscribe link to work remains questionable.
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The unsubscribe link is how spammers know that the autogenerated email address they are sending to is read by a human being. It makes the address more valuable when sold to another spammer. That one spammer may stop sending you messages from the same brand, to avoid landing in blacklists, but his other brands and his affiliates will be sending you more.
The US is a bit different from the rest of the world since US law (the Yes-You-Can-Spam act) requires that US-based spammers include and respect an unsubscribe link. Neither requirement is actively enforced, so the question of whether one can expect an unsubscribe link to work remains questionable.