What you should be doing when this happens is first MARK IT AS SPAM. This will quickly shuffle it out of your inbox and in to the spam folder where it will be dealt with by being noted as such. The problem is this may take days before it actually makes a difference and in some cases, not at all. This is where you will find yourself using the intended method of 'unsubscribing' from the email. The key to this is knowing when it is unsolicited mail or mail that was actually sent to your email address. You can usually tell by scrolling to the bottom of the message and looking for the UNSUBSCRIBE link. When you click on it, you should end up at a page that already has your email address included and may provide you with a short form asking you what mail you want to unsubscribe from, or the flow amount from daily to weekly, etc.
Now here's the important part of the unsubscribe process. When you clicked on that UNSUBSCRIBE ink near the bottom of the email you received and landed on a page that includes your email address, that is ok to continue however if you end up on a page that is now prompting you to ENTER YOUR EMAIL ADDRESS, you DO NOT want to proceed because if you do, you are going to find yourself signing up for even more email. This is unsolicited email whereas they send a blanket message out in hopes that you will open it and even better, attempt to unsubscribe and provide them with the legitimate email address (It's always about getting real live active email accounts to these spammers).. Just don't continue and note this email as SPAM.. nothing more you can do with this one... hopefully with the good spam rules built in to your gmail account, marking it as spam will correct this in the future.
I am writing this post in hopes it will help with SOME of the spam that does not get filtered to the spam folder, quite possibly because at one time you actually did sign up for whatever it is you are now getting and/or something you got is now sending on behalf of... regardless, using the UNSUBSCRIBE feature works best in these cases. Just don't be fooled and start entering in your email address, thinking that by doing so you will be successfully unsubscribing yourself from the mailer because you are going to only be making things worse for yourself.
I would say I have a 1 in 5 chance that this will actually work but a 4 in 5 chance that it will when it is actual email that I was once subscribed to. You see, the gmail spam filter works very good but has troubles filtering spam when you are legitimately subscribed to something so it can always help the system out when you have the ability to manually opt-out of some mailers.
