[BUGFIX] Use sender header configuration for optin and disclaimer e-mails

Related: #1321

Author: mschwemer

Classes/Domain/Service/Mail/SendMailService.php

@@ -290,9 +290,13 @@ protected function addPlainBody(MailMessage $message, array $email): MailMessage
     protected function addSenderHeader(MailMessage $message): MailMessage
     {
         if ($this->type === 'sender') {
-            $senderHeaderConfig= $this->configuration['sender.']['senderHeader.']??[];
+            $senderHeaderConfig= $this->configuration['sender.']['senderHeader.'] ?? [];
         } elseif ($this->type === 'receiver') {
-            $senderHeaderConfig = $this->settings['receiver.']['senderHeader.']??[];
+            $senderHeaderConfig = $this->settings['receiver.']['senderHeader.'] ?? [];
+        } elseif ($this->type === 'optin') {
+            $senderHeaderConfig = $this->configuration['optin.']['senderHeader.'] ?? [];
+        } elseif ($this->type === 'disclaimer') {
+            $senderHeaderConfig = $this->configuration['disclaimer.']['senderHeader.'] ?? [];
         }
 
         $email = ObjectUtility::getContentObject()->cObjGetSingle(