diff --git a/Application/Controller/Admin/MailCheckMenu.php b/Application/Controller/Admin/MailCheckMenu.php
index 01330e6..c820211 100644
--- a/Application/Controller/Admin/MailCheckMenu.php
+++ b/Application/Controller/Admin/MailCheckMenu.php
@@ -22,7 +22,7 @@ class MailCheckMenu extends AdminListController
 {
     protected $_sThisTemplate = '@'.Constants::OXID_MODULE_ID.'/admin/mailCheckMenu';
 
-    public function render()
+    public function render(): string
     {
         $this->setEditObjectId('foo');
         return parent::render();
diff --git a/Application/Controller/Admin/MailConfigCheck.php b/Application/Controller/Admin/MailConfigCheck.php
index e96ef82..e481b8a 100644
--- a/Application/Controller/Admin/MailConfigCheck.php
+++ b/Application/Controller/Admin/MailConfigCheck.php
@@ -26,9 +26,9 @@ use OxidEsales\Eshop\Core\Registry;
 class MailConfigCheck extends AdminDetailsController
 {
     protected $_sThisTemplate = '@'.Constants::OXID_MODULE_ID.'/admin/mailConfigCheck';
-    protected $testMailAddress = 'test@example.com';
+    protected string $testMailAddress = 'test@example.com';
 
-    public function render()
+    public function render(): string
     {
         $this->checkDataAreSet();
         $this->addTplParam('shop', Registry::getConfig()->getActiveShop());
@@ -36,7 +36,7 @@ class MailConfigCheck extends AdminDetailsController
         return parent::render();
     }
 
-    protected function checkDataAreSet()
+    protected function checkDataAreSet(): void
     {
         try {
             /** @var Shop $shop */
@@ -64,12 +64,12 @@ class MailConfigCheck extends AdminDetailsController
         }
     }
 
-    public function checkConfiguration()
+    public function checkConfiguration(): void
     {
         $this->getCurrentMailer();
     }
 
-    protected function getCurrentMailer()
+    protected function getCurrentMailer(): void
     {
         try {
 			$shop = Registry::getConfig()->getActiveShop();
diff --git a/Application/Controller/Admin/MailTester.php b/Application/Controller/Admin/MailTester.php
index 670d8cf..7723405 100644
--- a/Application/Controller/Admin/MailTester.php
+++ b/Application/Controller/Admin/MailTester.php
@@ -16,6 +16,7 @@ namespace D3\MailConfigChecker\Application\Controller\Admin;
 use Assert\Assert;
 use D3\MailConfigChecker\Application\Model\Constants;
 use D3\MailConfigChecker\Application\Model\Exception\d3TranslatableLazyAssertionException;
+use Exception;
 use OxidEsales\Eshop\Application\Controller\Admin\AdminDetailsController;
 use OxidEsales\Eshop\Application\Model\Shop;
 use OxidEsales\Eshop\Core\Email;
@@ -25,7 +26,7 @@ class MailTester extends AdminDetailsController
 {
     protected $_sThisTemplate = '@'.Constants::OXID_MODULE_ID.'/admin/mailTester';
 
-    public function sendMail()
+    public function sendMail(): void
     {
         try {
             $request = Registry::getRequest();
@@ -45,12 +46,12 @@ class MailTester extends AdminDetailsController
             $mail->setFrom($from);
             $mail->sendEmail($to, $subject, $body);
             $this->addTplParam('success', true);
-        } catch (\Exception $e) {
+        } catch ( Exception $e) {
             Registry::getUtilsView()->addErrorToDisplay(nl2br($e->getMessage()));
         }
     }
 
-    protected function assertContent()
+    protected function assertContent(): void
     {
         $request = Registry::getRequest();
         $lang = Registry::getLang();
@@ -76,7 +77,7 @@ class MailTester extends AdminDetailsController
             ->verifyNow();
     }
 
-    public function getMailAddressList()
+    public function getMailAddressList(): array
     {
         /** @var Shop $shop */
         $shop = Registry::getConfig()->getActiveShop();
diff --git a/Application/Controller/Admin/SmtpChecker.php b/Application/Controller/Admin/SmtpChecker.php
index 311a8f3..0793ec0 100644
--- a/Application/Controller/Admin/SmtpChecker.php
+++ b/Application/Controller/Admin/SmtpChecker.php
@@ -27,18 +27,18 @@ use PEAR_Error;
 
 class SmtpChecker extends AdminDetailsController
 {
-    protected $debug = true;
+    protected bool $debug = true;
 
-    protected $host;
-    protected $port;
-    protected $user;
-    protected $pwd;
-    protected $from;
-    protected $to;
+    protected string $host;
+    protected int $port;
+    protected string $user;
+    protected string $pwd;
+    protected string $from;
+    protected ?string $to = null;
 
-    protected $smtp;
-    protected $action;
-    protected $log = [];
+    protected Net_SMTP $smtp;
+    protected string $action = '';
+    protected array $log = [];
 
     public function __construct()
     {
@@ -69,19 +69,19 @@ class SmtpChecker extends AdminDetailsController
         $this->addTplParam('smtpLog', $this->log);
     }
 
-    public function getTemplateName()
+    public function getTemplateName(): string
     {
         return '@'.Constants::OXID_MODULE_ID.'/admin/smtpCheck';
     }
 
-    public function render()
+    public function render(): ?string
     {
         $this->addTplParam('shop', Registry::getConfig()->getActiveShop());
 
         return parent::render();
     }
 
-    public function getMailAddressList()
+    public function getMailAddressList(): array
     {
         /** @var Shop $shop */
         $shop = Registry::getConfig()->getActiveShop();
@@ -97,7 +97,7 @@ class SmtpChecker extends AdminDetailsController
         );
     }
 
-    public function sendMail()
+    public function sendMail(): void
     {
         try {
             $this->hostIsAvailable();
@@ -120,7 +120,7 @@ class SmtpChecker extends AdminDetailsController
      * @throws InvalidArgumentException
      * @return void
      */
-    protected function hostIsAvailable()
+    protected function hostIsAvailable(): void
     {
         $this->action = __FUNCTION__;
         Assert::that(
@@ -133,7 +133,7 @@ class SmtpChecker extends AdminDetailsController
         $this->smtp->setDebug($this->debug, [$this, 'dumpDebug']);
     }
 
-    protected function connect()
+    protected function connect(): void
     {
         $this->action = __FUNCTION__;
         Assert::that(
@@ -150,7 +150,7 @@ class SmtpChecker extends AdminDetailsController
      * @throws InvalidArgumentException
      * @return void
      */
-    protected function auth()
+    protected function auth(): void
     {
         $this->action = __FUNCTION__;
         Assert::that(
@@ -163,7 +163,7 @@ class SmtpChecker extends AdminDetailsController
         );
     }
 
-    protected function setFrom()
+    protected function setFrom(): void
     {
         $this->action = __FUNCTION__;
         Assert::that(
@@ -176,8 +176,12 @@ class SmtpChecker extends AdminDetailsController
         );
     }
 
-    protected function setRecipient()
+    protected function setRecipient(): void
     {
+        if (!$this->to) {
+            return;
+        }
+
         $this->action = __FUNCTION__;
         Assert::that(
             $this->smtp->rcptTo($this->to),
@@ -189,7 +193,7 @@ class SmtpChecker extends AdminDetailsController
         );
     }
 
-    protected function sendContent()
+    protected function sendContent(): void
     {
         if (!Registry::getRequest()->getRequestEscapedParameter('sendmail')) {
             return;
@@ -208,13 +212,13 @@ class SmtpChecker extends AdminDetailsController
         );
     }
 
-    protected function disconnect()
+    protected function disconnect(): void
     {
         $this->action = __FUNCTION__;
         $this->smtp->disconnect();
     }
 
-    public function dumpDebug($smtp, $message)
+    public function dumpDebug($smtp, $message): void
     {
         unset($smtp);
 
@@ -224,7 +228,7 @@ class SmtpChecker extends AdminDetailsController
         $this->log[$this->action][] = trim(htmlentities($message));
     }
 
-    public function formatMessage(array $arguments)
+    public function formatMessage(array $arguments): ?string
     {
         /** @var PEAR_Error|true $response */
         $response = $arguments['value'];
diff --git a/Application/Controller/Admin/SpfChecker.php b/Application/Controller/Admin/SpfChecker.php
index 3388cee..728ddc3 100644
--- a/Application/Controller/Admin/SpfChecker.php
+++ b/Application/Controller/Admin/SpfChecker.php
@@ -21,6 +21,7 @@ use D3\MailAuthenticationCheck\Model\DMARCResult;
 use D3\MailConfigChecker\Application\Model\Constants;
 use D3\MailConfigChecker\Application\Model\DmarcResult as OxDmarcResult;
 use D3\MailConfigChecker\Application\Model\SpfResult;
+use LogicException;
 use Mika56\SPFCheck\DNS\DNSRecordGetter;
 use Mika56\SPFCheck\Model\Query;
 use Mika56\SPFCheck\Model\Result;
@@ -33,14 +34,14 @@ class SpfChecker extends AdminDetailsController
 {
     protected $_sThisTemplate = '@'.Constants::OXID_MODULE_ID.'/admin/spfCheck';
 
-    public function render()
+    public function render(): ?string
     {
         $this->checkSpf();
         $this->checkDmarc();
         return parent::render();
     }
 
-    protected function checkSpf()
+    protected function checkSpf(): void
     {
         $result = [];
         $mailDomains = $this->getMailDomains();
@@ -54,7 +55,7 @@ class SpfChecker extends AdminDetailsController
         $this->addTplParam('spf_result', $result);
     }
 
-    protected function checkDmarc()
+    protected function checkDmarc(): void
     {
         $result = [];
         $mailDomains = $this->getMailDomains();
@@ -80,13 +81,13 @@ class SpfChecker extends AdminDetailsController
                         function ($mailAddress) {
                             $mailAddress = trim($mailAddress);
                             try {
-                                if (! strstr($mailAddress, '@')) {
+                                if ( ! str_contains( $mailAddress, '@' ) ) {
                                     throw oxNew(InvalidArgumentException::class);
                                 }
                                 $addressChunks = explode('@', $mailAddress);
 
                                 return array_pop($addressChunks);
-                            } catch (InvalidArgumentException $e) {
+                            } catch (InvalidArgumentException) {
                                 return '';
                             }
                         },
@@ -100,25 +101,17 @@ class SpfChecker extends AdminDetailsController
             );
     }
 
-    protected function checkSpfByDomain($domain, &$summarize)
+    protected function checkSpfByDomain($domain, &$summarize): void
     {
         $checker = new SPFCheck(new DNSRecordGetter());
         $query = new Query('', $domain);
 
         $result = $checker->getResult($query);
-        switch ($result->getResult()) {
-            case Result::FAIL:
-            case Result::NEUTRAL:
-            case Result::PASS:
-            case Result::SOFTFAIL:
-                $status = SpfResult::SET;
-                break;
-            case Result::NONE:
-                $status = SpfResult::MISSING;
-                break;
-            default:
-                $status = SpfResult::ERROR;
-        }
+        $status = match ( $result->getResult() ) {
+            Result::FAIL, Result::NEUTRAL, Result::PASS, Result::SOFTFAIL => SpfResult::SET,
+            Result::NONE => SpfResult::MISSING,
+            default => SpfResult::ERROR,
+        };
 
         $rawRecord = ($record = $result->getRecord()) ?
             $record->getRawRecord() :
@@ -127,52 +120,40 @@ class SpfChecker extends AdminDetailsController
         $summarize[$domain] = oxNew(SpfResult::class, $status, $rawRecord);
     }
 
-    public function getSpfStatusColor(SpfResult $result)
+    public function getSpfStatusColor(SpfResult $result): string
     {
-        switch ($result->getStatus()) {
-            case SpfResult::SET:
-                return 'success';
-            case SpfResult::ERROR:
-                return 'warning';
-            default:
-                return 'danger';
-        }
+        return match ( $result->getStatus() ) {
+            SpfResult::SET => 'success',
+            SpfResult::ERROR => 'warning',
+            default => 'danger',
+        };
     }
 
-    public function checkDmarcByDomain($domain, &$summarize)
+    public function checkDmarcByDomain($domain, &$summarize): void
     {
         try {
             $check = new DMARCCheck(new DNSRecordGetter());
             $query = new Query('', $domain);
             $record = $check->getResult($query)->getRecord();
 
-            switch ( $record->getRejectPolicy()->getValue() ) {
-                case DMARCResult::REJECT_QUARANTINE:
-                case DMARCResult::REJECT_REJECT:
-                    $status = OxDmarcResult::SET;
-                    break;
-                case DMARCResult::REJECT_NONE:
-                    $status = OxDmarcResult::MISSING;
-                    break;
-                default:
-                    $status = OxDmarcResult::ERROR;
-            }
+            $status = match ( $record->getRejectPolicy()->getValue() ) {
+                DMARCResult::REJECT_QUARANTINE, DMARCResult::REJECT_REJECT => OxDmarcResult::SET,
+                DMARCResult::REJECT_NONE => OxDmarcResult::MISSING,
+                default => OxDmarcResult::ERROR,
+            };
 
             $summarize[$domain] = oxNew( OxDmarcResult::class, $status, $record->getRawRecord());
-        } catch (\LogicException) {
+        } catch ( LogicException) {
             $summarize[$domain] = oxNew( OxDmarcResult::class, OxDmarcResult::MISSING, '');
         }
     }
 
-    public function getDmarcStatusColor(OxDmarcResult $result)
+    public function getDmarcStatusColor(OxDmarcResult $result): string
     {
-        switch ($result->getStatus()) {
-            case SpfResult::SET:
-                return 'success';
-            case SpfResult::ERROR:
-                return 'warning';
-            default:
-                return 'danger';
-        }
+        return match ( $result->getStatus() ) {
+            SpfResult::SET => 'success',
+            SpfResult::ERROR => 'warning',
+            default => 'danger',
+        };
     }
 }
diff --git a/Application/Model/DmarcResult.php b/Application/Model/DmarcResult.php
index 5d6e0a4..c32f1fb 100644
--- a/Application/Model/DmarcResult.php
+++ b/Application/Model/DmarcResult.php
@@ -30,12 +30,12 @@ class DmarcResult
         $this->record = $record;
     }
 
-    public function getStatus()
+    public function getStatus(): string
     {
         return $this->status;
     }
 
-    public function getRecord()
+    public function getRecord(): ?string
     {
         return $this->record;
     }
diff --git a/Application/Model/SpfResult.php b/Application/Model/SpfResult.php
index e8e1cfe..28bb255 100644
--- a/Application/Model/SpfResult.php
+++ b/Application/Model/SpfResult.php
@@ -21,8 +21,8 @@ class SpfResult
     public const MISSING   = 'missing';
     public const ERROR     = 'error';
 
-    protected $status;
-    protected $record;
+    protected string $status;
+    protected ?string $record;
 
     public function __construct(string $status, ?string $record = null)
     {
@@ -30,12 +30,12 @@ class SpfResult
         $this->record = $record;
     }
 
-    public function getStatus()
+    public function getStatus(): string
     {
         return $this->status;
     }
 
-    public function getRecord()
+    public function getRecord(): ?string
     {
         return $this->record;
     }
diff --git a/composer.json b/composer.json
index 3458ebf..7731668 100644
--- a/composer.json
+++ b/composer.json
@@ -34,6 +34,7 @@
     "oxid-esales/oxideshop-ce": "7.0 - 7.1",
     "pear/net_smtp": "^1.11",
     "mika56/spfcheck": "^2.1.1",
+    "d3/mailauthenticationcheck": "^0.1.0",
     "beberlei/assert": "^3.3"
   },
   "require-dev": {