diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5bdd8002d..d68808224 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+- [PR-391](https://github.com/itk-dev/os2loop/pull/391)
+  Mail development setup
 
 ## [1.3.1]
 
diff --git a/docker-compose.yml b/docker-compose.yml
index 230ab5a47..cd2af25f2 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -38,7 +38,7 @@ services:
       - PHP_MAX_EXECUTION_TIME=30
       - PHP_MEMORY_LIMIT=256M
       # Depending on the setup, you may have to remove --read-envelope-from from msmtp (cf. https://marlam.de/msmtp/msmtp.html) or use SMTP to send mail
-      - PHP_SENDMAIL_PATH=/usr/bin/msmtp --host=mail --port=1025 --read-recipients --read-envelope-from
+      - PHP_SENDMAIL_PATH=/usr/bin/msmtp --host=mail --port=1025 --read-recipients
       - DOCKER_HOST_DOMAIN=${COMPOSE_DOMAIN:?}
       - PHP_IDE_CONFIG=serverName=localhost
       # Let drush know the site uri (makes using --uri redundant)
diff --git a/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/drush.services.yml b/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/drush.services.yml
new file mode 100644
index 000000000..e1eaad45c
--- /dev/null
+++ b/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/drush.services.yml
@@ -0,0 +1,7 @@
+services:
+  os2loop_mail_notifications.send_mail:
+    class: Drupal\os2loop_mail_notifications\Command\SendMailCommand
+    arguments:
+      - "@plugin.manager.mail"
+    tags:
+      - { name: console.command }
diff --git a/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Command/SendMailCommand.php b/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Command/SendMailCommand.php
new file mode 100644
index 000000000..0f115aba0
--- /dev/null
+++ b/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Command/SendMailCommand.php
@@ -0,0 +1,103 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\os2loop_mail_notifications\Command;
+
+use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Mail\MailManagerInterface;
+use Drupal\node\Entity\Node;
+use Symfony\Component\Console\Attribute\AsCommand;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Exception\InvalidArgumentException;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Console\Style\SymfonyStyle;
+use Symfony\Component\Yaml\Yaml;
+
+// phpcs:disable Drupal.Commenting.ClassComment.Missing
+#[AsCommand(
+  name: 'os2loop_mail_notifications:mail:send',
+  description: 'Send a mail',
+  aliases: ['example'],
+)]
+final class SendMailCommand extends Command {
+
+  public function __construct(
+    private readonly MailManagerInterface $mailManager,
+  ) {
+    parent::__construct();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function configure() {
+    $this
+      ->addArgument('to', InputArgument::REQUIRED, 'The mail recipient')
+      ->addOption('module', NULL, InputOption::VALUE_REQUIRED, 'The module', 'os2loop_flag_content')
+      ->addOption('key', NULL, InputOption::VALUE_REQUIRED, 'The key', 'flag_content')
+      ->addOption('langcode', NULL, InputOption::VALUE_REQUIRED, 'The langcode', 'en')
+      ->addOption('params', NULL, InputOption::VALUE_REQUIRED, 'The params (whatever that may be) as a Yaml object', '{}')
+      ->setHelp(<<<HELP
+Examples:
+
+drush %command.name% test@example.com --params '
+message: My test message
+'
+HELP);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function execute(InputInterface $input, OutputInterface $output): int {
+    $io = new SymfonyStyle($input, $output);
+
+    $to = $input->getArgument('to');
+    $module = $input->getOption('module');
+    $key = $input->getOption('key');
+    $langcode = $input->getOption('langcode');
+    try {
+      $params = Yaml::parse($input->getOption('params'));
+    }
+    catch (\Exception $e) {
+      throw new InvalidArgumentException(dt('Invalid params: %message', ['%message' => $e->getMessage()]));
+    }
+
+    // @todo Add some useful stuff here.
+    $defaultParams = match ($module) {
+      'os2loop_flag_content' => [
+        'reason' => 'reason',
+        'message' => __FILE__,
+        'node' => Node::create([
+          'type' => 'test',
+          'nid' => 0,
+          'title' => __FILE__,
+        ]),
+      ],
+      default => throw new InvalidArgumentException(dt('Unknown module: %module', ['%module' => $module])),
+    };
+
+    $params = NestedArray::mergeDeep($defaultParams, (array) $params);
+
+    $send = TRUE;
+    $result = $this->mailManager->mail($module, $key, $to, $langcode, $params, NULL, $send);
+
+    $success = $result['result'] ?? FALSE;
+    if ($success) {
+      $io->success(dt('Mail successfully sent to %to', ['%to' => $to]));
+    }
+    else {
+      $io->error(dt('Error sending mail to %to', ['%to' => $to]));
+    }
+
+    // Show the message data.
+    $io->writeln(Yaml::dump($result));
+
+    return $success ? self::SUCCESS : self::FAILURE;
+  }
+
+}
diff --git a/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Plugin/Mail/PhpMail.php b/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Plugin/Mail/PhpMail.php
index e7a7e740d..86e96d744 100644
--- a/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Plugin/Mail/PhpMail.php
+++ b/web/profiles/custom/os2loop/modules/os2loop_mail_notifications/src/Plugin/Mail/PhpMail.php
@@ -11,7 +11,7 @@
  *
  * @Mail(
  *   id = "os2loop_mail_notifications",
- *   label = @Translation("Custom PHP mailer"),
+ *   label = @Translation("OS2Loop mail notifications"),
  *   description = @Translation("Sends the message as plain text, using PHP's native mail() function.")
  * )
  */