How can I stop emails from norton@nortonfromsymantec.com telling me that I've lost my PC protection?

I've been getting an automated email from this address for over a month wanting me to buy a license for the software.  I already have an active license.  The problem is that nowhere in their email does it say where I can opt-out of from getting these messages.  The send the email at least weekly and it's frustrating not being able stop it.

 

Does anyone know the best way to stop these emails?