diff --git a/Classes/Command/EmailCommandController.php b/Classes/Command/EmailCommandController.php
index d5149dd..f93bcc0 100644
--- a/Classes/Command/EmailCommandController.php
+++ b/Classes/Command/EmailCommandController.php
@@ -25,10 +25,10 @@ class EmailCommandController extends CommandController
      * @param string $to The to address of the message
      * @param string $subject The subject of the message
      * @param string $body The body of the message
-     * @param string $contentType The body content type of the message (Default: test/plain)
+     * @param string $contentType The body content type of the message (Default: text/plain)
      * @param string $charset The body charset of the message (Default: UTF8)
      */
-    public function sendCommand(string $from, string $to, string $subject, string $body = '', string $contentType = 'text/plain', $charset = 'UTF8'): void
+    public function sendCommand(string $from, string $to, string $subject, string $body = '', string $contentType = 'text/plain', string $charset = 'UTF8'): void
     {
         $message = (new Message())
             ->setFrom($from)
diff --git a/Classes/Mailer.php b/Classes/Mailer.php
index ac3a487..20b7f32 100644
--- a/Classes/Mailer.php
+++ b/Classes/Mailer.php
@@ -1,4 +1,6 @@
 <?php
+declare(strict_types=1);
+
 namespace Neos\SwiftMailer;
 
 /*
diff --git a/Classes/MailerInterface.php b/Classes/MailerInterface.php
index 76277c3..9750a47 100644
--- a/Classes/MailerInterface.php
+++ b/Classes/MailerInterface.php
@@ -29,25 +29,16 @@ interface MailerInterface
      *
      * The return value is the number of recipients who were accepted for
      * delivery.
-     *
-     * @param \Swift_Mime_SimpleMessage $message
-     * @param array $failedRecipients An array of failures by-reference
-     * @return int
      */
-    public function send(\Swift_Mime_SimpleMessage $message, &$failedRecipients = null);
+    public function send(\Swift_Mime_SimpleMessage $message, array &$failedRecipients = null);
 
     /**
      * Register a plugin using a known unique key (e.g. myPlugin).
-     *
-     * @param \Swift_Events_EventListener $plugin
-     * @return void
      */
     public function registerPlugin(\Swift_Events_EventListener $plugin);
 
     /**
      * The Transport used to send messages.
-     *
-     * @return \Swift_Transport
      */
     public function getTransport();
 }
diff --git a/Classes/Message.php b/Classes/Message.php
index 9170992..82e29d3 100644
--- a/Classes/Message.php
+++ b/Classes/Message.php
@@ -25,23 +25,18 @@ class Message extends \Swift_Message
 {
     /**
      * @Flow\Inject
-     * @var \Neos\SwiftMailer\MailerInterface
      */
-    protected $mailer;
+    protected MailerInterface $mailer;
 
     /**
      * True if the message has been sent.
-     *
-     * @var bool
      */
-    protected $sent = false;
+    protected bool $sent = false;
 
     /**
      * Holds the failed recipients after the message has been sent
-     *
-     * @var array
      */
-    protected $failedRecipients = [];
+    protected array $failedRecipients = [];
 
     /**
      * Sends the message.
@@ -57,8 +52,6 @@ public function send(): int
 
     /**
      * Checks whether the message has been sent.
-     *
-     * @return bool
      */
     public function isSent(): bool
     {
@@ -67,8 +60,6 @@ public function isSent(): bool
 
     /**
      * Returns the recipients for which the mail was not accepted for delivery.
-     *
-     * @return array the recipients who were not accepted for delivery
      */
     public function getFailedRecipients(): array
     {
diff --git a/Classes/Transport/LoggingTransport.php b/Classes/Transport/LoggingTransport.php
index c10690b..41541ae 100644
--- a/Classes/Transport/LoggingTransport.php
+++ b/Classes/Transport/LoggingTransport.php
@@ -26,21 +26,16 @@ class LoggingTransport implements TransportInterface
 {
     /**
      * Store sent messages for testing
-     *
-     * @var array
      */
-    protected static $deliveredMessages = [];
+    protected static array $deliveredMessages = [];
 
     /**
      * @Flow\Inject
-     * @var LoggerInterface
      */
-    protected $logger;
+    protected LoggerInterface $logger;
 
     /**
      * The logging transport is always started
-     *
-     * @return bool Always true for this transport
      */
     public function isStarted(): bool
     {
@@ -49,8 +44,6 @@ public function isStarted(): bool
 
     /**
      * No op
-     *
-     * @return void
      */
     public function start(): void
     {
@@ -58,8 +51,6 @@ public function start(): void
 
     /**
      * No op
-     *
-     * @return void
      */
     public function stop(): void
     {
@@ -68,10 +59,6 @@ public function stop(): void
     /**
      * "Send" the given Message. This transport will add it to a stored collection of sent messages
      * for testing purposes and log the message to the system logger.
-     *
-     * @param \Swift_Mime_SimpleMessage $message The message to send
-     * @param array &$failedRecipients Failed recipients
-     * @return int
      */
     public function send(\Swift_Mime_SimpleMessage $message, &$failedRecipients = null): int
     {
@@ -106,9 +93,6 @@ protected function buildStringFromEmailAndNameArray(array $addresses): string
 
     /**
      * No op
-     *
-     * @param \Swift_Events_EventListener $plugin
-     * @return void
      */
     public function registerPlugin(\Swift_Events_EventListener $plugin): void
     {
@@ -116,8 +100,6 @@ public function registerPlugin(\Swift_Events_EventListener $plugin): void
 
     /**
      * Get delivered messages that were sent through this transport
-     *
-     * @return array
      */
     public static function getDeliveredMessages(): array
     {
@@ -126,8 +108,6 @@ public static function getDeliveredMessages(): array
 
     /**
      * Reset the delivered messages (e.g. for tearDown in functional test)
-     *
-     * @return void
      */
     public static function reset(): void
     {
@@ -135,9 +115,7 @@ public static function reset(): void
     }
 
     /**
-     * Check if this Transport mechanism is alive.
-     *
-     * @return bool Always true for this transport
+     * This Transport mechanism is always alive.
      */
     public function ping(): bool
     {
diff --git a/Classes/Transport/MboxTransport.php b/Classes/Transport/MboxTransport.php
index 71b285b..76ec585 100644
--- a/Classes/Transport/MboxTransport.php
+++ b/Classes/Transport/MboxTransport.php
@@ -24,15 +24,12 @@
 class MboxTransport implements TransportInterface
 {
     /**
-     * @var string The file to write the mails into
+     * The file to write the mails into
      */
-    protected $mboxPathAndFilename;
+    protected string $mboxPathAndFilename;
 
     /**
      * Set path and filename of mbox file to use.
-     *
-     * @param string $mboxPathAndFilename
-     * @return void
      */
     public function setMboxPathAndFilename(string $mboxPathAndFilename): void
     {
@@ -41,8 +38,6 @@ public function setMboxPathAndFilename(string $mboxPathAndFilename): void
 
     /**
      * The mbox transport is always started
-     *
-     * @return boolean Always TRUE for this transport
      */
     public function isStarted(): bool
     {
@@ -51,8 +46,6 @@ public function isStarted(): bool
 
     /**
      * No op
-     *
-     * @return void
      */
     public function start(): void
     {
@@ -60,8 +53,6 @@ public function start(): void
 
     /**
      * No op
-     *
-     * @return void
      */
     public function stop(): void
     {
@@ -69,12 +60,8 @@ public function stop(): void
 
     /**
      * Outputs the mail to a text file according to RFC 4155.
-     *
-     * @param \Swift_Mime_SimpleMessage $message The message to send
-     * @param array &$failedRecipients Failed recipients (no failures in this transport)
-     * @return int
      */
-    public function send(\Swift_Mime_SimpleMessage $message, &$failedRecipients = null)
+    public function send(\Swift_Mime_SimpleMessage $message, &$failedRecipients = null): int
     {
         $message->generateId();
 
@@ -96,9 +83,6 @@ public function send(\Swift_Mime_SimpleMessage $message, &$failedRecipients = nu
 
     /**
      * Determine the best-use reverse path for this message
-     *
-     * @param \Swift_Mime_SimpleMessage $message
-     * @return string|null
      */
     private function getReversePath(\Swift_Mime_SimpleMessage $message): string
     {
@@ -123,18 +107,13 @@ private function getReversePath(\Swift_Mime_SimpleMessage $message): string
 
     /**
      * No op
-     *
-     * @param \Swift_Events_EventListener $plugin
-     * @return void
      */
     public function registerPlugin(\Swift_Events_EventListener $plugin): void
     {
     }
 
     /**
-     * Check if this Transport mechanism is alive.
-     *
-     * @return bool Always true for this transport
+     * This Transport mechanism is always alive.
      */
     public function ping(): bool
     {
diff --git a/Classes/TransportFactory.php b/Classes/TransportFactory.php
index d07a320..dd4e47a 100644
--- a/Classes/TransportFactory.php
+++ b/Classes/TransportFactory.php
@@ -24,22 +24,18 @@ class TransportFactory
     /**
      * Factory method which creates the specified transport with the given options.
      *
-     * @param string $transportType Object name of the transport to create
-     * @param array $transportOptions Options for the transport
-     * @param array $transportArguments Constructor arguments for the transport
-     * @return \Swift_Transport The created transport instance
      * @throws Exception
      * @throws \ReflectionException
      */
-    public function create(string $transportType, array $transportOptions = [], array $transportArguments = null): \Swift_Transport
+    public function create(string $transportType, array $transportOptions = [], array $transportConstructorArguments = null): \Swift_Transport
     {
         if (!class_exists($transportType)) {
             throw new Exception(sprintf('The specified transport backend "%s" does not exist.', $transportType), 1269351207);
         }
 
-        if (is_array($transportArguments)) {
+        if (is_array($transportConstructorArguments)) {
             $class = new \ReflectionClass($transportType);
-            $transport = $class->newInstanceArgs($transportArguments);
+            $transport = $class->newInstanceArgs($transportConstructorArguments);
         } else {
             $transport = new $transportType();
         }
diff --git a/Migrations/Code/Version20161130105617.php b/Migrations/Code/Version20161130105617.php
index 99536f7..26da176 100644
--- a/Migrations/Code/Version20161130105617.php
+++ b/Migrations/Code/Version20161130105617.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 
 namespace Neos\Flow\Core\Migrations;
 
@@ -17,7 +18,7 @@
  */
 class Version20161130105617 extends AbstractMigration
 {
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         return 'Neos.SwiftMailer-20161130105617';
     }
@@ -25,7 +26,7 @@ public function getIdentifier()
     /**
      * @return void
      */
-    public function up()
+    public function up(): void
     {
         $this->searchAndReplace('TYPO3\SwiftMailer', 'Neos\SwiftMailer');
         $this->searchAndReplace('TYPO3.SwiftMailer', 'Neos.SwiftMailer');
diff --git a/composer.json b/composer.json
index b369496..0a78707 100644
--- a/composer.json
+++ b/composer.json
@@ -6,8 +6,8 @@
         "MIT"
     ],
     "require": {
-        "neos/flow": "^5.2 || ^6.0 || ^7.0 || ^8.0 ||dev-master",
-        "swiftmailer/swiftmailer": "^6.0"
+        "neos/flow": "^8.3 || ^9.0 || dev-main",
+        "swiftmailer/swiftmailer": "^6.2.5"
     },
     "autoload": {
         "psr-4": {