diff --git a/config/config.sample.php b/config/config.sample.php
index 7a86070c18fe8..299e67c98fe23 100644
--- a/config/config.sample.php
+++ b/config/config.sample.php
@@ -421,6 +421,13 @@
  */
 'mail_send_plaintext_only' => false,
 
+/**
+ * This depends on ``mail_smtpmode``. Array of additional streams options that
+ * will be passed to underlying Swift mailer implementation.
+ * Defaults to an empty array.
+ */
+'mail_smtpstreamoptions' => array(),
+
 /**
  * Which mode is used for sendmail/qmail: ``smtp`` or ``pipe``.
  *
diff --git a/lib/private/Mail/Mailer.php b/lib/private/Mail/Mailer.php
index 7a8b4ad2599f3..b9f97bd9d95c1 100644
--- a/lib/private/Mail/Mailer.php
+++ b/lib/private/Mail/Mailer.php
@@ -259,6 +259,10 @@ protected function getSmtpInstance(): \Swift_SmtpTransport {
 		if (!empty($smtpSecurity)) {
 			$transport->setEncryption($smtpSecurity);
 		}
+		$streamingOptions = $this->config->getSystemValue('mail_smtpstreamoptions', array());
+		if (count($streamingOptions) > 0) {
+			$transport->setStreamOptions($streamingOptions);
+		}
 
 		return $transport;
 	}
diff --git a/tests/lib/Mail/MailerTest.php b/tests/lib/Mail/MailerTest.php
index 4117498885c35..97df9784f6ca8 100644
--- a/tests/lib/Mail/MailerTest.php
+++ b/tests/lib/Mail/MailerTest.php
@@ -167,4 +167,15 @@ public function testCreateEMailTemplate() {
 
 		$this->assertSame(EMailTemplate::class, get_class($this->mailer->createEMailTemplate('tests.MailerTest')));
 	}
+
+	public function testStreamingOptions() {
+		$this->config->method('getSystemValue')
+			->will($this->returnValueMap([
+				['mail_smtpmode', 'smtp', 'smtp'],
+				['mail_smtpstreamoptions', array(), array('foo' => 1)]
+			]));
+		$mailer = self::invokePrivate($this->mailer, 'getInstance');
+		$this->assertEquals(1, count($mailer->getTransport()->getStreamOptions()));
+		$this->assertTrue(isset($mailer->getTransport()->getStreamOptions()['foo']));
+	}
 }