function isValidEmail(sEmailAddress)
{
    var regexPattern = /[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}/i;
    
    if(sEmailAddress.match(regexPattern))
        return true;
    else
        return false;
}

function CustomEmailValidator(sender, args) {
    if (isValidEmail(args.Value))
        args.IsValid = true;
    else
        args.IsValid = false;
}