Welcome to Android Central! You can't. If those emails have an Unsubscribe option, don't click it -- it will likely get you even more spam. If your email provider has a good spam filter, just let your spam inbox fill up with that junk, and empty it periodically.
You're getting that junk because you registered on a certain website (which doesn't necessarily have to be porn). I suggest setting aside one of your email accounts to be your "junk" account for registration. Don't use your primary email account.