feat: add "null" SMTP transport mode

apps/settings/templates/settings/admin/additional-mail.php

@@ -34,6 +34,13 @@
 ?>
 
 <div class="section" id="mail_general_settings">
+<?php if ($_['mail_smtpmode'] === 'null') { ?>
+	<h2><?php p($l->t('Email server'));?></h2>
+
+	<p>
+	 <?php p($l->t('Mail delivery is disabled by instance config "%s".', ['mail_smtpmode'])); ?>
+	</p>
+<?php } else { ?>
 	<form id="mail_general_settings_form" class="mail_settings">
 		<h2><?php p($l->t('Email server'));?></h2>
 		<a 	target="_blank"
@@ -143,4 +150,5 @@
 	<em><?php p($l->t('Test and verify email settings')); ?></em>
 	<input type="submit" name="sendtestemail" id="sendtestemail" value="<?php p($l->t('Send email')); ?>"/>
 	<span id="sendtestmail_msg" class="msg"></span>
+<?php } ?>
 </div>

config/config.sample.php

@@ -521,7 +521,7 @@
 'mail_smtpdebug' => false,
 
 /**
- * Which mode to use for sending mail: ``sendmail``, ``smtp`` or ``qmail``.
+ * Which mode to use for sending mail: ``sendmail``, ``smtp``, ``qmail`` or ``null``.
  *
  * If you are using local or remote SMTP, set this to ``smtp``.
  *
@@ -531,6 +531,9 @@
  * For ``qmail`` the binary is /var/qmail/bin/sendmail, and it must be installed
  * on your Unix system.
  *
+ * Use the string ``null`` to send no mails (disable mail delivery). This can be
+ * useful if mails should be sent via APIs and rendering messages is not necessary.
+ *
  * Defaults to ``smtp``
  */
 'mail_smtpmode' => 'smtp',

lib/private/Mail/Mailer.php

@@ -27,6 +27,7 @@
 use Symfony\Component\Mailer\Exception\TransportExceptionInterface;
 use Symfony\Component\Mailer\Mailer as SymfonyMailer;
 use Symfony\Component\Mailer\MailerInterface;
+use Symfony\Component\Mailer\Transport\NullTransport;
 use Symfony\Component\Mailer\Transport\SendmailTransport;
 use Symfony\Component\Mailer\Transport\Smtp\EsmtpTransport;
 use Symfony\Component\Mailer\Transport\Smtp\Stream\SocketStream;
@@ -255,9 +256,10 @@ protected function getInstance(): MailerInterface {
 			return $this->instance;
 		}
 
-		$transport = null;
-
 		switch ($this->config->getSystemValueString('mail_smtpmode', 'smtp')) {
+			case 'null':
+				$transport = new NullTransport();
+				break;
 			case 'sendmail':
 				$transport = $this->getSendMailInstance();
 				break;
@@ -267,7 +269,9 @@ protected function getInstance(): MailerInterface {
 				break;
 		}
 
-		return new SymfonyMailer($transport);
+		$this->instance = new SymfonyMailer($transport);
+
+		return $this->instance;
 	}
 
 	/**

tests/lib/Mail/MailerTest.php

@@ -114,6 +114,26 @@ public function testGetSendmailInstanceSendMailQmail($sendmailMode, $binaryParam
 		$this->assertEquals($sendmail, self::invokePrivate($this->mailer, 'getSendMailInstance'));
 	}
 
+	public function testEventForNullTransport(): void {
+		$this->config
+			->expects($this->exactly(1))
+			->method('getSystemValueString')
+			->with('mail_smtpmode', 'smtp')
+			->willReturn('null');
+
+		$message = $this->createMock(Message::class);
+		$message->expects($this->once())
+			->method('getSymfonyEmail')
+			->willReturn((new Email())->to('foo@bar.com')->from('bar@foo.com')->text(''));
+
+		$event = new BeforeMessageSent($message);
+		$this->dispatcher->expects($this->once())
+			->method('dispatchTyped')
+			->with($this->equalTo($event));
+
+		$this->mailer->send($message);
+	}
+
 	public function testGetInstanceDefault(): void {
 		$this->config
 			->method('getSystemValue')
@@ -337,4 +357,10 @@ public function testLocalDomainInvalidUrl(): void {
 		self::assertInstanceOf(EsmtpTransport::class, $transport);
 		self::assertEquals('[127.0.0.1]', $transport->getLocalDomain());
 	}
+
+	public function testCaching(): void {
+		$symfonyMailer1 = self::invokePrivate($this->mailer, 'getInstance');
+		$symfonyMailer2 = self::invokePrivate($this->mailer, 'getInstance');
+		self::assertSame($symfonyMailer1, $symfonyMailer2);
+	}
 }