So lets just say you manage a mailing list of several hundred or thousands of folks. Now for whatever reason some folks don't like to get your very informative and witty newsletter. Special thanks to Dana Martens for the answer to the question. :-)

You can have recipients click an unsubscribe link in the Campaign e-mail and it will set their record to no longer receive E-mail marketing material.  Then when you create a Campaign, they will not receive the e-mail even if they are a member of the list you selected.  To set this up click Settings | Organization Settings | System Settings.  Click the Marketing tab and then set the auto-unsubscribe settings:

 

You can edit the Acknowledgement E-mail template to say whatever you want it to say.  Then when you are creating an E-mail in a Campaign you can type some text at the bottom of the e-mail such as “Click here to no longer receive marketing material.”  Then highlight the text and click the Unsubscribe button that appears in the formatting toolbar within the e-mail and it will change the text to a hyperlink.  When they click that link in the e-mail it will change the Send Marketing Materials field in their record from Yes to No and will also send them the acknowledgement e-mail to let them know they have been removed from the marketing list.