It wont cost them money if they have a double opt-in. But you will punish those without the double opt-in by pushing them up to the next tier in the payment plan sooner. The amount of money they waste one one dodgy email address is minuscule though. What is more funny is that they will see &lt;expletive&gt;@&lt;expletive&gt;.&lt;expletive&gt; when scrolling through their list, and you could even send them a &#x27;message&#x27; this way. E.g. WhyTheHellYouMakeMeSignUpForThisRubbish@fakeemail.com.