diff --git a/plugins/bc-mail/src/Controller/Admin/MailMessagesController.php b/plugins/bc-mail/src/Controller/Admin/MailMessagesController.php
index b759698b92..3ccf5bed9d 100644
--- a/plugins/bc-mail/src/Controller/Admin/MailMessagesController.php
+++ b/plugins/bc-mail/src/Controller/Admin/MailMessagesController.php
@@ -163,6 +163,7 @@ public function delete(
      * @return void
      * @checked
      * @noTodo
+     * @unitTest
      */
     public function attachment(MailMessagesServiceInterface $service)
     {
@@ -189,7 +190,6 @@ public function attachment(MailMessagesServiceInterface $service)
         }
         Header(sprintf('Content-type: %s; name=%s', $mineType, $file));
         echo file_get_contents($filePath);
-        exit();
     }
 
     /**
diff --git a/plugins/bc-mail/tests/TestCase/Controller/Admin/MailMessagesControllerTest.php b/plugins/bc-mail/tests/TestCase/Controller/Admin/MailMessagesControllerTest.php
index ac0ac55444..56d9c04280 100644
--- a/plugins/bc-mail/tests/TestCase/Controller/Admin/MailMessagesControllerTest.php
+++ b/plugins/bc-mail/tests/TestCase/Controller/Admin/MailMessagesControllerTest.php
@@ -207,7 +207,24 @@ public function testDelete()
      */
     public function testAttachment()
     {
-        $this->markTestIncomplete('このテストは、まだ実装されていません。');
+        $this->enableSecurityToken();
+        $this->enableCsrfToken();
+
+        $MailMessagesService = $this->getService(MailMessagesServiceInterface::class);
+        $MailMessagesService->createTable(1);
+        MailContentFactory::make(['id' => 1])->persist();
+        ContentFactory::make(['name' => 'name_test', 'plugin' => 'BcMail', 'type' => 'MailContent', 'entity_id' => 1])->persist();
+        $mailMessageTable = TableRegistry::getTableLocator()->get('mail_message_1');
+        $mailMessageTable->save(new Entity(['id' => 1, 'created' => '2016-07-29 18:02:53', 'modified' => '2020-09-14 21:10:41']));
+        $mailMessageTable->save(new Entity(['id' => 2, 'created' => '2016-07-29 18:02:53', 'modified' => '2020-09-14 21:10:41']));
+
+        ob_start();
+        $this->get('/baser/admin/bc-mail/mail_messages/attachment/1/00000002_tel.jpg');
+        $actualIsHelp = ob_get_clean();
+        $this->assertNotEmpty($actualIsHelp);
+
+        //不要テーブルを削除
+        $MailMessagesService->dropTable(1);
     }
 
     /**