How can I prevent surveys going to anyone outside my organisation.

I have tried to set a survey exclusion  

Exclude Survey when any of the following criteria is matched

e-mail ID does not contain mycompany.com

I have also tried

e-mail ID does not contain @mycompany.com

and also in desperation

e-mail id contains gmail.com 

This is being ignored and Surveys are still being sent on closure of every ticket