diff --git a/lib/private/Mail/Mailer.php b/lib/private/Mail/Mailer.php
index 3637bb1e27d70..0590f3db12a5f 100644
--- a/lib/private/Mail/Mailer.php
+++ b/lib/private/Mail/Mailer.php
@@ -204,7 +204,7 @@ public function validateMailAddress($email) {
 	 * @return string Converted mail address if `idn_to_ascii` exists
 	 */
 	protected function convertEmail($email) {
-		if (!function_exists('idn_to_ascii') || strpos($email, '@') === false) {
+		if (!function_exists('idn_to_ascii') || !defined('INTL_IDNA_VARIANT_UTS46') || strpos($email, '@') === false) {
 			return $email;
 		}
 
diff --git a/lib/private/Mail/Message.php b/lib/private/Mail/Message.php
index c695f0f4fb10f..4d9458fbd4056 100644
--- a/lib/private/Mail/Message.php
+++ b/lib/private/Mail/Message.php
@@ -65,7 +65,7 @@ public function attach(IAttachment $attachment) {
 	 * @return array Converted addresses if `idn_to_ascii` exists
 	 */
 	protected function convertAddresses($addresses) {
-		if (!function_exists('idn_to_ascii')) {
+		if (!function_exists('idn_to_ascii') || !defined('INTL_IDNA_VARIANT_UTS46')) {
 			return $addresses;
 		}