Spam or not spam?

Hi,

 

I received an email purporting to come from Norton, offering me a free computer tune-up as a thank you for my custom.

While discussing this with a "chat" service agent, she said that this would not have emanated from Norton, was probably spam and a security concern. Later the same day, while discussing it with another agent (each approached regarding different issues) he said that it was not spam and originated form Norton.

Has anyone any idea of how I may resolve the uncertainty and discover whether the invitation email was or was not genuine?

Many thanks for your help.