I do receive a lot of emails about lots of products and in most cases i tend to open them before discarding them.

In most cases spam is the greatest problem of email marketing but it has proven to be a very effective method of marketing.

Leaving an option to unsubscribe is one thing i know is always on most marketing mails even when you did not subscribe to them also after subscribing, you still see emails from the same address and then you wonder if the unsubscribe button isn't working.