What are opt-ins and opt-outs, and how are they supported?

The CAN-SPAM Act requires that users be allowed to opt out of an email marketing list. Keeping "clean" permission-based lists by making opt-outs easy is also a very good practice to follow.  

When a recipient of an email from BombBomb decides they no longer want to receive the emails they subscribed to, they can opt out by selecting an unsubscribe link at the bottom of the email.

For example, if the recipient no longer wishes to receive emails from NotSoTastyWineCorp.com, it would be helpful to have their name removed from all of the companies lists at once including the Red, White, and Sparkling email lists.