A custom Validate script for the field could look like:
// Custom Validate script
(function () {
var sDomain = "example.com";
// Don't do anything if field is blank
if (!event.value) return;
// Get the domain of the entered address, if any
var sEnteredDomain = event.value.split("@")[1];
if (typeof sEnteredDomain === "undefined" || sEnteredDomain.toLowerCase() !== sDomain) {
// Reject the entry
event.rc = false;
// Alert the user
app.alert("Please enter a valid email address.\r\rDomain must be: " + sDomain, 3);
}
})();
