This is the main global riddle, but somehow there are email newsletters from various sites in your Inbox. I did not signup and you did not sign up, and still here they are.
This is autotranslated version of this post.
Unsubscribe Gmail emails in bulk for Google Chrome will help massively to unsubscribe from newsletters in Gmail.
After installing the extension in Gmail you will see the new Unsubscribe button. You just need to choose emails and click on it.
The rest service will do for you. Perhaps the only disadvantage of this scheme is the registration through Gmail helpdesk service HelpNinja.