diff --git a/src/app/Policy/Greylist/Request.php b/src/app/Policy/Greylist/Request.php
--- a/src/app/Policy/Greylist/Request.php
+++ b/src/app/Policy/Greylist/Request.php
@@ -242,7 +242,7 @@
     {
         $recipients = \App\Utils::findObjectsByRecipientAddress($this->request['recipient']);
 
-        if (sizeof($recipients) > 1) {
+        if (count($recipients) > 1) {
             \Log::warning(
                 "Only taking the first recipient from the request for {$this->request['recipient']}"
             );
@@ -250,11 +250,9 @@
 
         if (count($recipients) >= 1) {
             foreach ($recipients as $recipient) {
-                if ($recipient) {
-                    $this->recipientID = $recipient->id;
-                    $this->recipientType = get_class($recipient);
-                    break;
-                }
+                $this->recipientID = $recipient->id;
+                $this->recipientType = get_class($recipient);
+                break;
             }
         } else {
             $recipient = null;
diff --git a/src/app/Utils.php b/src/app/Utils.php
--- a/src/app/Utils.php
+++ b/src/app/Utils.php
@@ -180,14 +180,18 @@
     /**
      * Find an object that is the recipient for the specified address.
      *
-     * @param string $address
+     * @param string $address E-mail address
      *
-     * @return array
+     * @return array<\App\User|\App\Resource|\App\SharedFolder> List of objects
      */
     public static function findObjectsByRecipientAddress($address)
     {
         $address = \App\Utils::normalizeAddress($address);
 
+        if (strpos($address, '@') === false) {
+            return [];
+        }
+
         list($local, $domainName) = explode('@', $address);
 
         $domain = \App\Domain::where('namespace', $domainName)->first();
@@ -196,34 +200,67 @@
             return [];
         }
 
+        // Find user/shared-folder/resource with specified address
+        // Note: Groups also have email address, but they aren't mailrecipients in LDAP
+
         $user = \App\User::where('email', $address)->first();
 
         if ($user) {
             return [$user];
         }
 
-        $userAliases = \App\UserAlias::where('alias', $address)->get();
+        $folder = \App\SharedFolder::where('email', $address)->first();
 
-        if (count($userAliases) > 0) {
-            $users = [];
+        if ($folder) {
+            return [$folder];
+        }
 
-            foreach ($userAliases as $userAlias) {
-                $users[] = $userAlias->user;
-            }
+        $resource = \App\Resource::where('email', $address)->first();
 
-            return $users;
+        if ($resource) {
+            return [$resource];
         }
 
-        $userAliases = \App\UserAlias::where('alias', "catchall@{$domain->namespace}")->get();
+        // Find aliases with specified address
+        // TODO: Folders and users can have the same alias, should we merge the result (and return both)?
 
-        if (count($userAliases) > 0) {
-            $users = [];
+        $users = \App\User::select('users.*')
+            ->join('user_aliases', 'user_aliases.user_id', '=', 'users.id')
+            ->where('alias', $address)
+            ->get();
 
-            foreach ($userAliases as $userAlias) {
-                $users[] = $userAlias->user;
-            }
+        if (count($users) > 0) {
+            return $users->all();
+        }
+
+        $folders = \App\SharedFolder::select('shared_folders.*')
+            ->join('shared_folder_aliases', 'shared_folder_aliases.shared_folder_id', '=', 'shared_folders.id')
+            ->where('alias', $address)
+            ->get();
+
+        if (count($folders) > 0) {
+            return $folders->all();
+        }
+
+        // Use catchall@ alias if exists
+        // TODO: Folders and users can have the same alias, should we merge the result (and return both)?
+
+        $users = \App\User::select('users.*')
+            ->join('user_aliases', 'user_aliases.user_id', '=', 'users.id')
+            ->where('alias', "catchall@{$domain->namespace}")
+            ->get();
+
+        if (count($users) > 0) {
+            return $users->all();
+        }
+
+        $folders = \App\SharedFolder::select('shared_folders.*')
+            ->join('shared_folder_aliases', 'shared_folder_aliases.shared_folder_id', '=', 'shared_folders.id')
+            ->where('alias', "catchall@{$domain->namespace}")
+            ->get();
 
-            return $users;
+        if (count($folders) > 0) {
+            return $folders->all();
         }
 
         return [];
diff --git a/src/tests/Feature/UtilsTest.php b/src/tests/Feature/UtilsTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Feature/UtilsTest.php
@@ -0,0 +1,111 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Domain;
+use App\Utils;
+use Tests\TestCase;
+
+class UtilsTest extends TestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        $this->deleteTestUser('UserAccountA@UserAccount.com');
+        $this->deleteTestDomain('UserAccount.com');
+        $this->deleteTestSharedFolder('folder-test@kolabnow.com');
+        $this->deleteTestResource('resource-test@kolabnow.com');
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function tearDown(): void
+    {
+        $this->deleteTestUser('UserAccountA@UserAccount.com');
+        $this->deleteTestDomain('UserAccount.com');
+        $this->deleteTestSharedFolder('folder-test@kolabnow.com');
+        $this->deleteTestResource('resource-test@kolabnow.com');
+
+        parent::tearDown();
+    }
+
+    /**
+     * Test Utils::findObjectsByRecipientAddress()
+     */
+    public function testFindObjectsByRecipientAddress(): void
+    {
+        $result = Utils::findObjectsByRecipientAddress('unknown');
+        $this->assertCount(0, $result);
+
+        $result = Utils::findObjectsByRecipientAddress('unknown@unknow.org');
+        $this->assertCount(0, $result);
+
+        $result = Utils::findObjectsByRecipientAddress('unknown@kolab.org');
+        $this->assertCount(0, $result);
+
+        // Users
+
+        $user = $this->getTestUser('UserAccountA@UserAccount.com');
+        $domain = $this->getTestDomain('UserAccount.com', [
+                'status' => Domain::STATUS_NEW | Domain::STATUS_ACTIVE,
+                'type' => Domain::TYPE_PUBLIC,
+        ]);
+
+        $result = Utils::findObjectsByRecipientAddress('UserAccountA@UserAccount.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($user->email, $result[0]->email);
+
+        $user->setAliases(['test@UserAccount.com']);
+
+        $result = Utils::findObjectsByRecipientAddress('test@UserAccount.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($user->email, $result[0]->email);
+
+        $user->setAliases(['catchall@UserAccount.com']);
+
+        $result = Utils::findObjectsByRecipientAddress('unknown@UserAccount.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($user->email, $result[0]->email);
+
+        // Shared folders
+
+        $folder = $this->getTestSharedFolder('folder-test@kolabnow.com');
+        $folder->setAliases(['test@kolabnow.com']);
+
+        $result = Utils::findObjectsByRecipientAddress('folder-test@kolabnow.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($folder->email, $result[0]->email);
+
+        $result = Utils::findObjectsByRecipientAddress('test@kolabnow.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($folder->email, $result[0]->email);
+
+        $folder->setAliases(['catchall@kolabnow.com']);
+
+        $result = Utils::findObjectsByRecipientAddress('unknown@kolabnow.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($folder->email, $result[0]->email);
+
+        // Resources
+
+        $resource = $this->getTestResource('resource-test@kolabnow.com');
+
+        $result = Utils::findObjectsByRecipientAddress('resource-test@kolabnow.com');
+
+        $this->assertCount(1, $result);
+        $this->assertSame($resource->email, $result[0]->email);
+
+        // TODO: Test multiple entries result
+    }
+}