unix – What e-mail program uses iWatch by default?

I'm trying to see what email program uses iWatch by default to send alerts after defining contact email addresses for specific alerts. I do not see the mail program defined in any of the configuration files, however, I see some iWatch documentation that discusses its raw usage in the configuration files, which somehow eliminates the point of having email addresses if iWatch does not define which email program to use. I can provide any of my configuration files as references if necessary.