Custom Action Application Ribbon CRM 2013 possible?

Hi Everyone,

I am trying to modify the "Send" button on the email activity.

I want it to reference a JavaScript which validates the contact's email addresses.

If conditions are met we want to send the email. Otherwise throw an error message.

I am trying to use the Ribbon Workbench CRM 2013 to do this.

However, it doesn't seem to be calling my JS.

Is this possible to do on a Application Ribbon??

Dave