非常感谢 @crazy4x 的解答：
后来我自己找到一个新的方法：

目标： 输入框输入多个邮箱地址的时候，检验N个邮箱地址是否正确并给出提示
方法：

HTML:
<form class="form-horizontal" role="form" id="custom_form" name="custom_form" novalidate>

        <p class="form-group">
            <label class="col-sm-2 control-label">email address</label>
            <p class="col-sm-10" ng-class="{'has-error':custom_form.user_email.$invalid&&custom_form.user_email.$dirty}">
                <input multiple-email name="user_email" ng-model="user.email" required class="form-control" placeholder="seperate the multiple mails with "
                /> 验证通过：{{custom_form.user_email.$valid}}
            </p>
        </p>
        <p class="form-group  text-center">
            <input class="btn btn-primary btn-lg" ng-disabled="custom_form.$invalid" type="submit" value="提交" />
        </p>
    </form>
    
    

Js:(Angular)

   app.directive('multipleEmail', [function () {
        return {
            require: "ngModel",
            link: function (scope, element, attr, ngModel) {
                if (ngModel) {
                    var emailsRegexp =
                        /^([a-z0-9!#$%&'*+\/=?^_`{|}~.-]+@[a-z0-9-]+(\.[a-z0-9-]+)*[;；]?)+$/i;
                }
                var customValidator = function (value) {
                    var validity = ngModel.$isEmpty(value) || emailsRegexp.test(value);
                    ngModel.$setValidity("multipleEmail", validity);
                    return validity ? value : undefined;
                };
                ngModel.$formatters.push(customValidator);
                ngModel.$parsers.push(customValidator);
            }
        };
    }]);