My ISP constantly sends me emails about "staying safe online" and "the holiday season". At the bottom of the email, it says "THIS IS A SERVICE-RELATED EMAIL", supposedly to excuse the lack of any unsubscribe link.

Unfortunately you are no longer allowed to take them to court over this, as their terms of service simply say you are no longer allowed to sue them :) just like all tech companies that know they're committing lawsuit-worthy offenses.