diff --git a/lib/private/Mail/Mailer.php b/lib/private/Mail/Mailer.php
index da3fcd35888..b0c08815f1e 100644
--- a/lib/private/Mail/Mailer.php
+++ b/lib/private/Mail/Mailer.php
@@ -267,7 +267,9 @@ class Mailer implements IMailer {
 				break;
 		}
 
-		return new SymfonyMailer($transport);
+		$this->instance = new SymfonyMailer($transport);
+
+		return $this->instance;
 	}
 
 	/**
diff --git a/tests/lib/Mail/MailerTest.php b/tests/lib/Mail/MailerTest.php
index f215e385e3f..84015f38d24 100644
--- a/tests/lib/Mail/MailerTest.php
+++ b/tests/lib/Mail/MailerTest.php
@@ -337,4 +337,10 @@ class MailerTest extends TestCase {
 		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);
+	}
 }