Default mail client not installed properly?

I am trying to email registrants to verify email adresses and when I go to users tab in dashboard I recieve a message that says the default email client is not properly installed. Does anyone know of a solution to this? I am sure its a pretty simple problem, I am just checking with my trusty wordpress forum experts before I take matters into my own hands. http://www.jwflyfishing.com Thanks in advance to all replies.
JW