Does unsubscribing to spam mail work?

The term spam and options to flag/report spam get misused and misunderstood too often.

True spam email comes from places you've never given you email address to or never agreed to receive email from. Pseudo spam is all of the junk/bulk mail and newsletters you get that you actually signed up for at some point, these emails have legitimate and trustworthy means of unsubscribing from the message. You should set up filters for or unsubscribe from pseudo spam rather than marking it as spam as the latter adversely effects your spam filters.

In true spam email, you should never click the link to unsubscribe or reply to the message to unsubscribe. The trick is differentiating between the real spam and the pseudo spam.

The CAN SPAM act has a bigger impact on the mailing practices of legitimate businesses that fall into the pseudo spam / bulk mailer category than the true spammers.

Another tactic is to bounce the email, but smart spammers can tell the difference between a user generated bounce and one generated bu the mail server.

Also realize that most bulk email, legitimate or not, uses link and image tracking to tell if the emails are being opened or the links clicked. To prevent this, you can set your email client to block the loading of remote images.