Other than using "email type" as a field, below background script always helped me for email validation.

Use this and customize wherever you need to validate email.

// Get email address from field
var emailAddress= "123gmail.com";

//If Email address is valid, take some aciton.For example printing success message below
if (/^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))+$/.test(emailAddress)){
gs.info("Valid Email Address");
}

//If Email address is not valid, stop form submission or take some action
else{
gs.info("The email address format is invalid");

}

Regards

Pawan K Singh