Run the following js code, choose the primary key of any delivery
var d = nms.delivery.load("841925965");
for (var i in d) {
logInfo([i]);
}
also you can log which mailparameter variables are available
var d = nms.delivery.load("841925965");
for (var i in d.mailParameters) {
logInfo([i]);
}

For instance, you can dynamically generate the delivery's subject line from within the workflow's delivery activity without modifying the template. ie.
delivery.mailParameters.subject = "Daily report for "+formatDate(new Date(), "%2D%2M%4Y");
