diff --git a/typo3/sysext/core/Classes/Mail/TransportFactory.php b/typo3/sysext/core/Classes/Mail/TransportFactory.php
index 1bd203bff6bd..636f946df851 100644
--- a/typo3/sysext/core/Classes/Mail/TransportFactory.php
+++ b/typo3/sysext/core/Classes/Mail/TransportFactory.php
@@ -58,7 +58,7 @@ public function get(array $mailSettings): \Swift_Transport
                     $host = $parts[0];
                     $port = $parts[1] ?? null;
                 } else {
-                    $host = (string)$mailSettings['transport_smtp_server'] ?? null;
+                    $host = (string)$mailSettings['transport_smtp_server'] ?? '';
                     $port = null;
                 }