diff --git a/assets/js/src/forms/list.jsx b/assets/js/src/forms/list.jsx
index 0fabf70d73..fa68480414 100644
--- a/assets/js/src/forms/list.jsx
+++ b/assets/js/src/forms/list.jsx
@@ -151,6 +151,10 @@ const FormList = React.createClass({
       return segment.name;
     }).join(', ');
 
+    if (form.settings.segments_selected_by === 'user') {
+      segments = MailPoet.I18n.t('userChoice') + ' ' + segments;
+    }
+
     return (
       <div>
         <td className={ row_classes }>
diff --git a/assets/js/src/public.js b/assets/js/src/public.js
index c998fac195..defbf2e02f 100644
--- a/assets/js/src/public.js
+++ b/assets/js/src/public.js
@@ -44,29 +44,36 @@ function(
               endpoint: 'subscribers',
               action: 'subscribe',
               data: data
+            }).fail(function(response) {
+              form.find('.mailpoet_validate_error').html(
+                response.errors.map(function(error) {
+                  return error.message;
+                }).join('<br />')
+              ).show();
             }).done(function(response) {
-              if(response.result === false) {
-                form.find('.mailpoet_validate_error').html(
-                  response.errors.join('<br />')
-                ).show();
+              // successfully subscribed
+              if (
+                response.meta !== undefined
+                && response.meta.redirect_url !== undefined
+              ) {
+                // go to page
+                window.location.href = response.meta.redirect_url;
               } else {
-                // successfully subscribed
-                if(response.page !== undefined) {
-                  // go to page
-                  window.location.href = response.page;
-                } else {
-                  // display success message
-                  form.find('.mailpoet_validate_success').show();
-                }
-
-                // reset form
-                form.trigger('reset');
-                // reset validation
-                parsley.reset();
+                // display success message
+                form.find('.mailpoet_validate_success').show();
               }
 
+              // reset form
+              form.trigger('reset');
+              // reset validation
+              parsley.reset();
+
               // resize iframe
-              if(window.frameElement !== null) {
+              if (
+                window.frameElement !== null
+                && MailPoet !== undefined
+                && MailPoet['Iframe']
+              ) {
                 MailPoet.Iframe.autoSize(window.frameElement);
               }
             });
diff --git a/lib/API/API.php b/lib/API/API.php
index 834206caec..65ac28213f 100644
--- a/lib/API/API.php
+++ b/lib/API/API.php
@@ -6,9 +6,6 @@ use \MailPoet\Util\Security;
 if(!defined('ABSPATH')) exit;
 
 class API {
-  function __construct() {
-  }
-
   function init() {
     // security token
     add_action(
@@ -27,7 +24,12 @@ class API {
       'wp_ajax_nopriv_mailpoet',
       array($this, 'setupPublic')
     );
+
     // Public API (Post)
+    add_action(
+      'admin_post_mailpoet',
+      array($this, 'setupPublic')
+    );
     add_action(
       'admin_post_nopriv_mailpoet',
       array($this, 'setupPublic')
@@ -102,12 +104,16 @@ class API {
     try {
       $endpoint = new $endpoint();
       $response = $endpoint->$method($data);
-      $response->send();
+      if($doing_ajax) {
+        $response->send();
+      }
     } catch(\Exception $e) {
-      $error_response = new ErrorResponse(
-        array($e->getCode() => $e->getMessage())
-      );
-      $error_response->send();
+      if($doing_ajax) {
+        $error_response = new ErrorResponse(
+          array($e->getCode() => $e->getMessage())
+        );
+        $error_response->send();
+      }
     }
   }
 
diff --git a/lib/API/Endpoints/CustomFields.php b/lib/API/Endpoints/CustomFields.php
index 1dcfa908b4..6fd6c14dfc 100644
--- a/lib/API/Endpoints/CustomFields.php
+++ b/lib/API/Endpoints/CustomFields.php
@@ -8,7 +8,7 @@ if(!defined('ABSPATH')) exit;
 
 class CustomFields extends APIEndpoint {
   function getAll() {
-    $collection = CustomField::findMany();
+    $collection = CustomField::orderByAsc('created_at')->findMany();
     $custom_fields = array_map(function($custom_field) {
       return $custom_field->asArray();
     }, $collection);
diff --git a/lib/API/Endpoints/Forms.php b/lib/API/Endpoints/Forms.php
index b552e25c8e..24f0835f3b 100644
--- a/lib/API/Endpoints/Forms.php
+++ b/lib/API/Endpoints/Forms.php
@@ -156,7 +156,6 @@ class Forms extends APIEndpoint {
     // check if the user gets to pick his own lists
     // or if it's selected by the admin
     $has_segment_selection = false;
-
     foreach($body as $i => $block) {
       if($block['type'] === 'segment') {
         $has_segment_selection = true;
@@ -164,7 +163,7 @@ class Forms extends APIEndpoint {
           $list_selection = array_filter(
             array_map(function($segment) {
               return (isset($segment['id'])
-                ? (int)$segment['id']
+                ? $segment['id']
                 : null
               );
             }, $block['params']['values'])
@@ -177,6 +176,7 @@ class Forms extends APIEndpoint {
     // check list selection
     if($has_segment_selection === true) {
       $settings['segments_selected_by'] = 'user';
+      $settings['segments'] = $list_selection;
     } else {
       $settings['segments_selected_by'] = 'admin';
     }
diff --git a/lib/API/Endpoints/Subscribers.php b/lib/API/Endpoints/Subscribers.php
index 20d066600a..a8a86ce36d 100644
--- a/lib/API/Endpoints/Subscribers.php
+++ b/lib/API/Endpoints/Subscribers.php
@@ -57,13 +57,9 @@ class Subscribers extends APIEndpoint {
 
   function subscribe($data = array()) {
     $doing_ajax = (bool)(defined('DOING_AJAX') && DOING_AJAX);
-    $errors = array();
-
-    $form = Form::findOne($data['form_id']);
+    $form_id = (isset($data['form_id']) ? (int)$data['form_id'] : false);
+    $form = Form::findOne($form_id);
     unset($data['form_id']);
-    if($form === false || !$form->id()) {
-      $errors[] = __('This form does not exist');
-    }
 
     $segment_ids = (!empty($data['segments'])
       ? (array)$data['segments']
@@ -72,71 +68,63 @@ class Subscribers extends APIEndpoint {
     unset($data['segments']);
 
     if(empty($segment_ids)) {
-      $errors[] = __('Please select a list');
-    }
-
-    if(!empty($errors)) {
-      return array(
-        'result' => false,
-        'errors' => $errors
-      );
+      if($doing_ajax) {
+        return $this->badRequest(array(
+          APIError::BAD_REQUEST => __('Please select a list')
+        ));
+      } else {
+        Url::redirectBack(array(
+          'mailpoet_error' => $form_id,
+          'mailpoet_success' => null
+        ));
+      }
     }
 
+    // try to register and subscribe user to segments
     $subscriber = Subscriber::subscribe($data, $segment_ids);
     $errors = $subscriber->getErrors();
-    $result = ($errors === false && $subscriber->id() > 0);
 
-    // record form statistics
-    if($result === true && $form !== false && $form->id > 0) {
-      StatisticsForms::record($form->id, $subscriber->id);
-    }
+    if($errors !== false) {
+      if($doing_ajax) {
+        return $this->badRequest($errors);
+      } else {
+        Url::redirectBack(array(
+          'mailpoet_error' => $form_id,
+          'mailpoet_success' => null
+        ));
+      }
+    } else {
+      $meta = array();
 
-    // get success message to display after subscription
-    $form_settings = (
-      isset($form->settings)
-      ? unserialize($form->settings)
-      : null
-    );
+      if($form !== false) {
+        // record form statistics
+        StatisticsForms::record($form->id, $subscriber->id);
 
-    if($form_settings !== null) {
-      switch($form_settings['on_success']) {
-        case 'page':
-          $success_page_url = get_permalink($form_settings['success_page']);
+        $form = $form->asArray();
 
-          // response depending on context
-          if($doing_ajax === true) {
-            return array(
-              'result' => $result,
-              'page' => $success_page_url,
-              'errors' => $errors
-            );
-          } else {
-            if($result === false) {
-              Url::redirectBack();
-            } else {
-              Url::redirectTo($success_page_url);
-            }
-          }
-          break;
+        if($form['settings']['on_success'] === 'page') {
+          // redirect to a page on a success, pass the page url in the meta
+          $meta['redirect_url'] = get_permalink($form['settings']['success_page']);
+        } else if($form['settings']['on_success'] === 'url') {
+          $meta['redirect_url'] = $form['settings']['success_url'];
+        }
+      }
 
-        case 'message':
-        default:
-          // response depending on context
-          if($doing_ajax === true) {
-            return array(
-              'result' => $result,
-              'errors' => $errors
-            );
-          } else {
-            $params = (
-              ($result === true)
-              ? array('mailpoet_success' => $form->id)
-              : array()
-            );
 
-            Url::redirectBack($params);
-          }
-          break;
+      if($doing_ajax) {
+        return $this->successResponse(
+          Subscriber::findOne($subscriber->id)->asArray(),
+          $meta
+        );
+      } else {
+        if(isset($meta['redirect_url'])) {
+          Url::redirectTo($meta['redirect_url']);
+        } else {
+          Url::redirectBack(array(
+            'mailpoet_success' => $form['id'],
+            'mailpoet_error' => null
+          ));
+        }
       }
     }
   }
diff --git a/lib/Form/Block/Checkbox.php b/lib/Form/Block/Checkbox.php
index 37c77bff64..b767a21eda 100644
--- a/lib/Form/Block/Checkbox.php
+++ b/lib/Form/Block/Checkbox.php
@@ -22,7 +22,6 @@ class Checkbox extends Base {
 
     foreach($options as $option) {
       $html .= '<label class="mailpoet_checkbox_label">';
-      $html .= '<input type="hidden" name="'.$field_name.'" value="0" />';
       $html .= '<input type="checkbox" class="mailpoet_checkbox" ';
 
       $html .= 'name="'.$field_name.'" ';
diff --git a/lib/Form/Util/Export.php b/lib/Form/Util/Export.php
index 05e61474c9..c49f9689bb 100644
--- a/lib/Form/Util/Export.php
+++ b/lib/Form/Util/Export.php
@@ -24,13 +24,14 @@ class Export {
         return join(' ', array(
           '<iframe',
           'width="100%"',
+          'height="100%"',
           'scrolling="no"',
           'frameborder="0"',
           'src="'.$iframe_url.'"',
           'class="mailpoet_form_iframe"',
           'vspace="0"',
           'tabindex="0"',
-          'onload="MailPoet.Iframe.autoSize(this);"',
+          'onload="if(window[\'MailPoet\']) MailPoet.Iframe.autoSize(this);"',
           'marginwidth="0"',
           'marginheight="0"',
           'hspace="0"',
diff --git a/lib/Form/Widget.php b/lib/Form/Widget.php
index ca06a58cd3..43e38d2d5c 100644
--- a/lib/Form/Widget.php
+++ b/lib/Form/Widget.php
@@ -8,6 +8,7 @@ use \MailPoet\Models\Subscriber;
 use \MailPoet\Form\Renderer as FormRenderer;
 use \MailPoet\Form\Util;
 use \MailPoet\Util\Security;
+use \MailPoet\Util\Url;
 
 if(!defined('ABSPATH')) exit;
 
@@ -148,12 +149,17 @@ class Widget extends \WP_Widget {
           'after_title' => (!empty($after_title) ? $after_title : '')
         );
 
-        // check if the form was successfully submitted via POST (non ajax)
+        // (POST) non ajax success/error variables
         $data['success'] = (
           (isset($_GET['mailpoet_success']))
           &&
           ((int)$_GET['mailpoet_success'] === (int)$form['id'])
         );
+        $data['error'] = (
+          (isset($_GET['mailpoet_error']))
+          &&
+          ((int)$_GET['mailpoet_error'] === (int)$form['id'])
+        );
 
         // generate security token
         $data['token'] = Security::generateToken();
diff --git a/lib/Models/Subscriber.php b/lib/Models/Subscriber.php
index d0e18128a9..e86b3b4ca2 100644
--- a/lib/Models/Subscriber.php
+++ b/lib/Models/Subscriber.php
@@ -73,72 +73,69 @@ class Subscriber extends Model {
   }
 
   function sendConfirmationEmail() {
-    if($this->status === self::STATUS_UNCONFIRMED) {
-      $signup_confirmation = Setting::getValue('signup_confirmation');
+    $signup_confirmation = Setting::getValue('signup_confirmation');
 
-      $segments = $this->segments()->findMany();
-      $segment_names = array_map(function($segment) {
-        return $segment->name;
-      }, $segments);
+    $segments = $this->segments()->findMany();
+    $segment_names = array_map(function($segment) {
+      return $segment->name;
+    }, $segments);
 
-      $body = nl2br($signup_confirmation['body']);
+    $body = nl2br($signup_confirmation['body']);
 
-      // replace list of segments shortcode
-      $body = str_replace(
-        '[lists_to_confirm]',
-        '<strong>'.join(', ', $segment_names).'</strong>',
-        $body
-      );
+    // replace list of segments shortcode
+    $body = str_replace(
+      '[lists_to_confirm]',
+      '<strong>'.join(', ', $segment_names).'</strong>',
+      $body
+    );
 
-      // replace activation link
-      $body = str_replace(
-        array(
-          '[activation_link]',
-          '[/activation_link]'
-        ),
-        array(
-          '<a href="'.esc_attr(Subscription\Url::getConfirmationUrl($this)).'">',
-          '</a>'
-        ),
-        $body
-      );
+    // replace activation link
+    $body = str_replace(
+      array(
+        '[activation_link]',
+        '[/activation_link]'
+      ),
+      array(
+        '<a href="'.esc_attr(Subscription\Url::getConfirmationUrl($this)).'">',
+        '</a>'
+      ),
+      $body
+    );
 
-      // build email data
-      $email = array(
-        'subject' => $signup_confirmation['subject'],
-        'body' => array(
-          'html' => $body,
-          'text' => $body
-        )
-      );
+    // build email data
+    $email = array(
+      'subject' => $signup_confirmation['subject'],
+      'body' => array(
+        'html' => $body,
+        'text' => $body
+      )
+    );
 
-      // convert subscriber to array
-      $subscriber = $this->asArray();
+    // convert subscriber to array
+    $subscriber = $this->asArray();
 
-      // set from
-      $from = (
-        !empty($signup_confirmation['from'])
-        && !empty($signup_confirmation['from']['address'])
-      ) ? $signup_confirmation['from']
-        : false;
+    // set from
+    $from = (
+      !empty($signup_confirmation['from'])
+      && !empty($signup_confirmation['from']['address'])
+    ) ? $signup_confirmation['from']
+      : false;
 
-      // set reply to
-      $reply_to = (
-        !empty($signup_confirmation['reply_to'])
-        && !empty($signup_confirmation['reply_to']['address'])
-      ) ? $signup_confirmation['reply_to']
-        : false;
+    // set reply to
+    $reply_to = (
+      !empty($signup_confirmation['reply_to'])
+      && !empty($signup_confirmation['reply_to']['address'])
+    ) ? $signup_confirmation['reply_to']
+      : false;
 
-      // send email
-      try {
-        $mailer = new Mailer(false, $from, $reply_to);
-        return $mailer->send($email, $subscriber);
-      } catch(\Exception $e) {
-        $this->setError($e->getMessage());
-        return false;
-      }
+    // send email
+    try {
+      $mailer = new Mailer(false, $from, $reply_to);
+      return $mailer->send($email, $subscriber);
+    } catch(\Exception $e) {
+      $this->setError($e->getMessage());
+      return false;
     }
-    return false;
   }
 
   static function generateToken($email = null) {
@@ -153,27 +150,30 @@ class Subscriber extends Model {
   }
 
   static function subscribe($subscriber_data = array(), $segment_ids = array()) {
-    if(empty($subscriber_data) or empty($segment_ids)) {
-      return false;
-    }
-
     $signup_confirmation_enabled = (bool)Setting::getValue(
       'signup_confirmation.enabled'
     );
 
-    $subscriber = self::createOrUpdate($subscriber_data);
-    $errors = $subscriber->getErrors();
+    $subscriber = self::findOne($subscriber_data['email']);
+
+    if($subscriber === false) {
+      // create new subscriber
+      $subscriber = self::createOrUpdate($subscriber_data);
+      if($subscriber->getErrors() !== false) {
+        return $subscriber;
+      }
 
-    if($errors === false && $subscriber->id > 0) {
       $subscriber = self::findOne($subscriber->id);
+    }
 
-      // restore deleted subscriber
+    if($subscriber !== false) {
+      // restore trashed subscriber
       if($subscriber->deleted_at !== null) {
         $subscriber->setExpr('deleted_at', 'NULL');
       }
 
+      // set status depending on signup confirmation setting
       if($subscriber->status !== self::STATUS_SUBSCRIBED) {
-        // auto subscribe when signup confirmation is disabled
         if($signup_confirmation_enabled === true) {
           $subscriber->set('status', self::STATUS_UNCONFIRMED);
         } else {
@@ -186,9 +186,7 @@ class Subscriber extends Model {
         SubscriberSegment::subscribeToSegments($subscriber, $segment_ids);
 
         // signup confirmation
-        if($subscriber->status !== self::STATUS_SUBSCRIBED) {
-          $subscriber->sendConfirmationEmail();
-        }
+        $subscriber->sendConfirmationEmail();
 
         // welcome email
         Scheduler::scheduleSubscriberWelcomeNotification(
diff --git a/views/form/editor.html b/views/form/editor.html
index 20b4be9d5a..3cf91f8dc0 100644
--- a/views/form/editor.html
+++ b/views/form/editor.html
@@ -274,18 +274,17 @@
         // form editor: default fields
         var template = Handlebars.compile($('#form_template_fields').html());
 
-        var data = {
-          fields: mailpoet_default_fields
-        };
-
         return MailPoet.Ajax.post({
           endpoint: 'customFields',
           action: 'getAll',
         }).done(function(response) {
-          data.fields  = $.merge(response.data, data.fields);
-
           // render toolbar
-          jQuery('#mailpoet_toolbar_fields').html(template(data));
+          jQuery('#mailpoet_toolbar_fields').html(template({
+            fields: $.merge(
+              $.merge([], mailpoet_default_fields),
+              response.data
+            )
+          }));
 
           setTimeout(function() {
             WysijaForm.init();
diff --git a/views/form/iframe.html b/views/form/iframe.html
index c9c45262df..9cbed9470e 100644
--- a/views/form/iframe.html
+++ b/views/form/iframe.html
@@ -20,25 +20,6 @@
     <%= form | raw %>
     <script type="text/javascript">
       var MailPoetForm = <%= json_encode(mailpoet_form) %>;
-      function autoSize() {
-        var iframe = window.frameElement;
-        var height = document.body.scrollHeight;
-        parent.MailPoet.Iframe.setSize(iframe, height);
-      }
-
-      jQuery(function($) {
-        $(function() {
-          autoSize();
-        });
-      });
-
-      jQuery('form').on('submit', function() {
-        setTimeout(function() {
-          // make sure we resize the iframe
-          autoSize();
-        }.bind(this), 1);
-        return true;
-      }.bind(this));
     </script>
   </body>
 </html>
\ No newline at end of file
diff --git a/views/form/widget.html b/views/form/widget.html
index b1846cfd58..8eb03b025a 100644
--- a/views/form/widget.html
+++ b/views/form/widget.html
@@ -30,11 +30,14 @@
           <% if not(success) %>
           style="display:none;"
           <% endif %>
-        >
-          <%= form.settings.success_message %>
-        </p>
-        <p class="mailpoet_validate_error" style="display:none;">
-          <!-- errors will be displayed here -->
+        ><%= form.settings.success_message %></p>
+        <p class="mailpoet_validate_error"
+          <% if not(error) %>
+          style="display:none;"
+          <% endif %>
+        ><% if (error) %>
+           <%= __("An error occurred, make sure you have filled all the required fields.") %>
+          <% endif %>
         </p>
       </div>
     </form>
diff --git a/views/forms.html b/views/forms.html
index 18a990185f..5320358b52 100644
--- a/views/forms.html
+++ b/views/forms.html
@@ -41,6 +41,7 @@
 
     'formName': __('Name'),
     'segments': __('Lists'),
+    'userChoice': __('User choice:'),
     'signups': __('Signups'),
     'createdOn': __('Created On'),
     'oneFormTrashed': __('1 form was moved to the trash'),