diff --git a/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/Headers/ParameterizedHeader.php b/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/Headers/ParameterizedHeader.php
index b4a0ddf1224..228946a5ee9 100644
--- a/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/Headers/ParameterizedHeader.php
+++ b/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/Headers/ParameterizedHeader.php
@@ -97,7 +97,7 @@ class Swift_Mime_Headers_ParameterizedHeader extends Swift_Mime_Headers_Unstruct
     {
         $params = $this->getParameters();
 
-        return $params[$parameter] ?? null;
+        return isset($params[$parameter]) ? $params[$parameter] : null;
     }
 
     /**
diff --git a/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMessage.php b/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMessage.php
index 768de07f812..f8667954bcf 100644
--- a/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMessage.php
+++ b/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMessage.php
@@ -493,7 +493,7 @@ class Swift_Mime_SimpleMessage extends Swift_Mime_MimePart
             '%[1-5]'
             );
 
-        return $priority ?? 3;
+        return isset($priority) ? $priority : 3;
     }
 
     /**
diff --git a/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMimeEntity.php b/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMimeEntity.php
index 2d1a9b47d56..a434729f613 100644
--- a/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMimeEntity.php
+++ b/htdocs/includes/swiftmailer/lib/classes/Swift/Mime/SimpleMimeEntity.php
@@ -293,7 +293,7 @@ class Swift_Mime_SimpleMimeEntity implements Swift_Mime_CharsetObserver, Swift_M
     public function setChildren(array $children, $compoundLevel = null)
     {
         // TODO: Try to refactor this logic
-        $compoundLevel = $compoundLevel ?? $this->getCompoundLevel($children);
+        $compoundLevel = isset($compoundLevel) ? $compoundLevel : $this->getCompoundLevel($children);
         $immediateChildren = array();
         $grandchildren = array();
         $newContentType = $this->userContentType;
diff --git a/htdocs/includes/swiftmailer/lib/classes/Swift/Plugins/DecoratorPlugin.php b/htdocs/includes/swiftmailer/lib/classes/Swift/Plugins/DecoratorPlugin.php
index 9d5feefb92c..745ee879003 100644
--- a/htdocs/includes/swiftmailer/lib/classes/Swift/Plugins/DecoratorPlugin.php
+++ b/htdocs/includes/swiftmailer/lib/classes/Swift/Plugins/DecoratorPlugin.php
@@ -159,7 +159,7 @@ class Swift_Plugins_DecoratorPlugin implements Swift_Events_SendListener, Swift_
             return $this->replacements->getReplacementsFor($address);
         }
 
-        return $this->replacements[$address] ?? null;
+        return isset($this->replacements[$address]) ? $this->replacements[$address] : null;
     }
 
     /**
diff --git a/htdocs/includes/swiftmailer/lib/classes/Swift/Transport/EsmtpTransport.php b/htdocs/includes/swiftmailer/lib/classes/Swift/Transport/EsmtpTransport.php
index 7eb7ef33086..56d9c748769 100644
--- a/htdocs/includes/swiftmailer/lib/classes/Swift/Transport/EsmtpTransport.php
+++ b/htdocs/includes/swiftmailer/lib/classes/Swift/Transport/EsmtpTransport.php
@@ -208,7 +208,7 @@ class Swift_Transport_EsmtpTransport extends Swift_Transport_AbstractSmtpTranspo
      */
     public function getSourceIp()
     {
-        return $this->params['sourceIp'] ?? null;
+        return isset($this->params['sourceIp']) ? $this->params['sourceIp'] : null;
     }
 
     /**