diff --git a/lib/private/Mail/Mailer.php b/lib/private/Mail/Mailer.php
index 05ef0bf513962..148a4f6f833ec 100644
--- a/lib/private/Mail/Mailer.php
+++ b/lib/private/Mail/Mailer.php
@@ -293,8 +293,8 @@ protected function getSmtpInstance(): EsmtpTransport {
 		// either null or true - if nothing is passed, let the symfony mailer figure out the configuration by itself
 		$mailSmtpsecure = ($this->config->getSystemValue('mail_smtpsecure', null) === 'ssl') ? true : null;
 		$transport = new EsmtpTransport(
-			$this->config->getSystemValue('mail_smtphost', '127.0.0.1'),
-			(int)$this->config->getSystemValue('mail_smtpport', 25),
+			$this->config->getSystemValueString('mail_smtphost', '127.0.0.1'),
+			$this->config->getSystemValueInt('mail_smtpport', 25),
 			$mailSmtpsecure,
 			null,
 			$this->logger
@@ -302,11 +302,11 @@ protected function getSmtpInstance(): EsmtpTransport {
 		/** @var SocketStream $stream */
 		$stream = $transport->getStream();
 		/** @psalm-suppress InternalMethod */
-		$stream->setTimeout($this->config->getSystemValue('mail_smtptimeout', 10));
+		$stream->setTimeout($this->config->getSystemValueInt('mail_smtptimeout', 10));
 
-		if ($this->config->getSystemValue('mail_smtpauth', false)) {
-			$transport->setUsername($this->config->getSystemValue('mail_smtpname', ''));
-			$transport->setPassword($this->config->getSystemValue('mail_smtppassword', ''));
+		if ($this->config->getSystemValueBool('mail_smtpauth', false)) {
+			$transport->setUsername($this->config->getSystemValueString('mail_smtpname', ''));
+			$transport->setPassword($this->config->getSystemValueString('mail_smtppassword', ''));
 		}
 
 		$streamingOptions = $this->config->getSystemValue('mail_smtpstreamoptions', []);
diff --git a/tests/lib/Mail/MailerTest.php b/tests/lib/Mail/MailerTest.php
index 39e4d689a3709..a93086a201fdd 100644
--- a/tests/lib/Mail/MailerTest.php
+++ b/tests/lib/Mail/MailerTest.php
@@ -239,9 +239,16 @@ public function testCreateEMailTemplate() {
 	public function testStreamingOptions() {
 		$this->config->method('getSystemValue')
 			->willReturnMap([
-				['mail_smtpmode', 'smtp', 'smtp'],
 				['mail_smtpstreamoptions', [], ['foo' => 1]],
+			]);
+		$this->config->method('getSystemValueString')
+			->willReturnMap([
+				['mail_smtpmode', 'smtp', 'smtp'],
+				['overwrite.cli.url', '', ''],
 				['mail_smtphost', '127.0.0.1', '127.0.0.1'],
+			]);
+		$this->config->method('getSystemValueInt')
+			->willReturnMap([
 				['mail_smtpport', 25, 25],
 				['mail_smtptimeout', 10, 10],
 			]);
@@ -256,12 +263,20 @@ public function testStreamingOptions() {
 	public function testStreamingOptionsWrongType() {
 		$this->config->method('getSystemValue')
 			->willReturnMap([
-				['mail_smtpmode', 'smtp', 'smtp'],
 				['mail_smtpstreamoptions', [], 'bar'],
+			]);
+		$this->config->method('getSystemValueString')
+			->willReturnMap([
+				['mail_smtpmode', 'smtp', 'smtp'],
+				['overwrite.cli.url', '', ''],
 				['mail_smtphost', '127.0.0.1', '127.0.0.1'],
+			]);
+		$this->config->method('getSystemValueInt')
+			->willReturnMap([
 				['mail_smtpport', 25, 25],
 				['mail_smtptimeout', 10, 10],
 			]);
+
 		$mailer = self::invokePrivate($this->mailer, 'getInstance');
 		/** @var EsmtpTransport $transport */
 		$transport = self::invokePrivate($mailer, 'transport');
@@ -270,16 +285,17 @@ public function testStreamingOptionsWrongType() {
 	}
 
 	public function testLocalDomain(): void {
-		$this->config->method('getSystemValue')
+		$this->config->method('getSystemValueString')
 			->willReturnMap([
 				['mail_smtpmode', 'smtp', 'smtp'],
+				['overwrite.cli.url', '', 'https://some.valid.url.com:8080'],
 				['mail_smtphost', '127.0.0.1', '127.0.0.1'],
+			]);
+		$this->config->method('getSystemValueInt')
+			->willReturnMap([
 				['mail_smtpport', 25, 25],
 				['mail_smtptimeout', 10, 10],
 			]);
-		$this->config->method('getSystemValueString')
-			->with('overwrite.cli.url', '')
-			->willReturn('https://some.valid.url.com:8080');
 
 		/** @var SymfonyMailer $mailer */
 		$mailer = self::invokePrivate($this->mailer, 'getInstance');
@@ -292,16 +308,17 @@ public function testLocalDomain(): void {
 	}
 
 	public function testLocalDomainInvalidUrl(): void {
-		$this->config->method('getSystemValue')
+		$this->config->method('getSystemValueString')
 			->willReturnMap([
 				['mail_smtpmode', 'smtp', 'smtp'],
+				['overwrite.cli.url', '', 'https:only.slash.does.not.work:8080'],
 				['mail_smtphost', '127.0.0.1', '127.0.0.1'],
+			]);
+		$this->config->method('getSystemValueInt')
+			->willReturnMap([
 				['mail_smtpport', 25, 25],
 				['mail_smtptimeout', 10, 10],
 			]);
-		$this->config->method('getSystemValueString')
-			->with('overwrite.cli.url', '')
-			->willReturn('https:only.slash.does.not.work:8080');
 
 		/** @var SymfonyMailer $mailer */
 		$mailer = self::invokePrivate($this->mailer, 'getInstance');