Issue #3262457 by balis_m, AdamPS: Cancel email sending

config/schema/symfony_mailer.schema.yml

@@ -134,6 +134,14 @@ symfony_mailer.email_adjuster_plugin.email_reply_to:
       type: label
       label: 'Display name'
 
+symfony_mailer.email_adjuster_plugin.email_skip_sending:
+  type: mapping
+  label: 'Skip sending'
+  mapping:
+    message:
+      type: label
+      label: 'Skip message'
+
 symfony_mailer.email_adjuster_plugin.email_subject:
   type: mapping
   label: 'Subject'

src/Exception/SkipMailException.php

+<?php
+
+namespace Drupal\symfony_mailer\Exception;
+
+/**
+ * Exception to cancel email sending.
+ */
+class SkipMailException extends \Exception {
+
+}

src/Mailer.php

@@ -15,6 +15,7 @@ use Drupal\Core\StringTranslation\StringTranslationTrait;
 use Drupal\Core\StringTranslation\TranslationManager;
 use Drupal\Core\Url;
 use Drupal\symfony_mailer\Exception\MissingTransportException;
+use Drupal\symfony_mailer\Exception\SkipMailException;
 use Symfony\Component\Mailer\Mailer as SymfonyMailer;
 use Symfony\Component\Mailer\Transport;
 use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
@@ -133,7 +134,16 @@ class Mailer implements MailerInterface {
     // to ensure it doesn't leak into the render context for the HTTP response
     // to the current request.
     return $this->renderer->executeInRenderContext(new RenderContext(), function () use ($email) {
-      return $this->doSend($email);
+      try {
+        return $this->doSend($email);
+      }
+      catch (SkipMailException $e) {
+        if ($this->account->hasPermission('administer mailer')) {
+          \Drupal::messenger()->addError($this->t('Email sending skipped: %message.', [
+            '%message' => $e->getMessage(),
+          ]));
+        }
+      }
     });
   }
 

src/Plugin/EmailAdjuster/SkipSendingEmailAdjuster.php

+<?php
+
+namespace Drupal\symfony_mailer\Plugin\EmailAdjuster;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\symfony_mailer\Processor\EmailAdjusterBase;
+use Drupal\symfony_mailer\EmailInterface;
+use Drupal\symfony_mailer\Exception\SkipMailException;
+
+/**
+ * Defines the Skip Sending Email Adjuster.
+ *
+ * @EmailAdjuster(
+ *   id = "email_skip_sending",
+ *   label = @Translation("Skip sending"),
+ *   description = @Translation("Skips the email sending."),
+ *   weight = -1,
+ * )
+ */
+class SkipSendingEmailAdjuster extends EmailAdjusterBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preBuild(EmailInterface $email) {
+    throw new SkipMailException($this->configuration['message']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsForm(array $form, FormStateInterface $form_state) {
+    $form['message'] = [
+      '#type' => 'textfield',
+      '#default_value' => $this->configuration['message'] ?? NULL,
+      '#description' => $this->t('Users with permission to manage mailer settings will see this message when skipping an email.'),
+    ];
+
+    return $form;
+  }
+
+}