diff --git a/src/Admin/GlobalController.php b/src/Admin/GlobalController.php
index d9a2d412..fc759f2c 100644
--- a/src/Admin/GlobalController.php
+++ b/src/Admin/GlobalController.php
@@ -176,13 +176,11 @@ class GlobalController extends ControllerBase {
             return $this->error(__('请输入有效的邮箱地址', 'aksrt'));
         }
 
-        $sent = class_exists('\\AKSRT\\Settings\\Mail')
-            ? \AKSRT\Settings\Mail::send_test_email($to)
-            : false;
-        if ($sent) {
-            return $this->success(['message' => '测试邮件已发送']);
+        $result = \AKSRT\Settings\Mail::send_test_email($to);
+        if (is_wp_error($result)) {
+            return $this->error(__('邮件发送失败，详细原因已写入服务器错误日志', 'aksrt'));
         }
-        return $this->error(__('邮件发送失败，请检查 SMTP 配置', 'aksrt'));
+        return $this->success(['message' => '测试邮件已发送']);
     }
 
     public function rest_homepage_tab_posts(\WP_REST_Request $request): \WP_REST_Response {
diff --git a/src/Settings/Mail.php b/src/Settings/Mail.php
index 6be372bf..27bfb740 100644
--- a/src/Settings/Mail.php
+++ b/src/Settings/Mail.php
@@ -10,24 +10,21 @@ namespace AKSRT\Settings;
 defined('ABSPATH') || exit;
 
 final class Mail {
-    /** @return list<string> */
-    public static function events(): array {
-        return array_keys(MailTemplates::definitions());
-    }
-
     /** @return array<string, mixed> */
     public static function get_smtp(): array {
         $s = Settings::get_all();
+        $username = trim((string) ($s['mail_smtp_name'] ?? '')) ?: sanitize_email((string) ($s['mail_name'] ?? ''));
+        $password = (string) ($s['mail_passwd'] ?? '');
         return [
             'enabled' => !empty($s['mail_smtps']),
             'host' => trim((string) ($s['mail_host'] ?? '')),
             'port' => max(1, min(65535, (int) ($s['mail_port'] ?? 465))),
-            'username' => trim((string) ($s['mail_smtp_name'] ?? '')) ?: sanitize_email((string) ($s['mail_name'] ?? '')),
-            'password' => (string) ($s['mail_passwd'] ?? ''),
+            'username' => $username,
+            'password' => $password,
             'encryption' => in_array(($s['mail_smtpsecure'] ?? 'ssl'), ['ssl', 'tls', ''], true) ? (string) ($s['mail_smtpsecure'] ?? 'ssl') : 'ssl',
             'from_name' => trim((string) ($s['mail_showname'] ?? '')) ?: get_bloginfo('name'),
             'from_address' => sanitize_email((string) ($s['mail_name'] ?? '')),
-            'auth' => !empty($s['mail_smtpauth']),
+            'auth' => $username !== '' && $password !== '',
         ];
     }
 
@@ -88,16 +85,25 @@ final class Mail {
         $definition = MailTemplates::definitions()[$event];
         $subject = (string) ($cfg['subject'] ?? $default_subject ?: $definition['title']);
         $content = (string) ($cfg['content'] ?? $default_content ?: $definition['content']);
-        $subject = self::replace_placeholders($subject, $placeholders, false);
-        $content = self::replace_placeholders($content, $placeholders, false);
+        $subject = self::replace_placeholders($subject, $placeholders);
+        $content = self::replace_placeholders($content, $placeholders);
         $content = self::wrap_html($content, $cfg['global'] ?? []);
         $headers = ['Content-Type: text/html; charset=UTF-8'];
         return (bool) wp_mail($to, $subject, $content, $headers);
     }
 
-    public static function send_test_email(string $to): bool {
+    public static function send_test_email(string $to): bool|\WP_Error {
         $to = sanitize_email($to);
-        if ($to === '' || !is_email($to)) return false;
+        if ($to === '' || !is_email($to)) {
+            return new \WP_Error('aksrt_invalid_test_email', __('请输入有效的邮箱地址', 'aksrt'));
+        }
+
+        $failure = null;
+        $capture_failure = static function (\WP_Error $error) use (&$failure): void {
+            $failure = $error;
+        };
+        add_action('wp_mail_failed', $capture_failure);
+
         $site = esc_html((string) get_bloginfo('name'));
         $subject = '邮件配置测试';
         $content = "您好，\n\n这是一封来自 {$site} 的邮件配置测试。";
@@ -105,7 +111,22 @@ final class Mail {
             'description' => '此信为系统邮件，请不要直接回复。',
             'more_content' => '',
         ]);
-        return (bool) wp_mail($to, $subject, $content, ['Content-Type: text/html; charset=UTF-8']);
+
+        try {
+            $sent = (bool) wp_mail($to, $subject, $content, ['Content-Type: text/html; charset=UTF-8']);
+        } finally {
+            remove_action('wp_mail_failed', $capture_failure);
+        }
+
+        if ($sent) {
+            return true;
+        }
+
+        $error = $failure instanceof \WP_Error
+            ? $failure
+            : new \WP_Error('aksrt_mail_failed', __('wp_mail 返回失败，但未提供详细错误。', 'aksrt'));
+        self::log_test_failure($error);
+        return $error;
     }
 
     /** @return array<string, mixed> */
@@ -121,20 +142,23 @@ final class Mail {
         ];
     }
 
-    private static function replace_placeholders(string $value, array $placeholders, bool $html): string {
+    private static function replace_placeholders(string $value, array $placeholders): string {
         $replace = [];
         foreach ($placeholders as $key => $replacement) {
-            $replacement = (string) $replacement;
-            if ($html) {
-                $replacement = str_contains($key, 'url') ? esc_url($replacement) : esc_html($replacement);
-            } else {
-                $replacement = wp_strip_all_tags($replacement);
-            }
-            $replace[$key] = $replacement;
+            $replace[$key] = wp_strip_all_tags((string) $replacement);
         }
         return strtr($value, $replace);
     }
 
+    private static function log_test_failure(\WP_Error $error): void {
+        $message = sanitize_text_field($error->get_error_message());
+        $message = preg_replace('/[A-Z0-9._%+\-]+@[A-Z0-9.\-]+\.[A-Z]{2,}/i', '[email]', $message);
+        $message = preg_replace('/\b(?:[a-z0-9-]+\.)+[a-z]{2,}\b/i', '[host]', (string) $message);
+        $message = preg_replace('/\b(?:\d{1,3}\.){3}\d{1,3}\b/', '[ip]', (string) $message);
+        $message = preg_replace('/\b(?:password|passwd|username|user|login|credential)\s*[:=]\s*[^\s,;]+/i', '$1=[redacted]', (string) $message);
+        error_log('[AKSRT] SMTP 测试失败：' . substr((string) $message, 0, 500));
+    }
+
     private static function wrap_html(string $content, array $global): string {
         $logo = method_exists(Settings::class, 'logo_url') ? Settings::logo_url() : '';
         $background = esc_url(AKSRT_URI . '/assets/img/mail-bg.png');
diff --git a/src/Settings/MailTemplates.php b/src/Settings/MailTemplates.php
index 3c666f4a..90279b2a 100644
--- a/src/Settings/MailTemplates.php
+++ b/src/Settings/MailTemplates.php
@@ -62,7 +62,6 @@ final class MailTemplates {
             'mail_smtp_name' => '',
             'mail_host' => '',
             'mail_port' => 465,
-            'mail_smtpauth' => true,
             'mail_smtpsecure' => 'ssl',
             'mail_showname' => $site,
             'mail_title_prefix' => '[' . $site . ']',
@@ -89,7 +88,6 @@ final class MailTemplates {
                 ['key' => 'mail_smtp_name', 'label' => 'SMTP 用户名', 'type' => 'input', 'default' => $defaults['mail_smtp_name'], 'dependsOn' => ['key' => 'mail_smtps', 'value' => true]],
                 ['key' => 'mail_host', 'label' => '邮件服务器地址', 'type' => 'input', 'default' => $defaults['mail_host'], 'dependsOn' => ['key' => 'mail_smtps', 'value' => true]],
                 ['key' => 'mail_port', 'label' => 'SMTP 服务器端口', 'type' => 'number', 'default' => $defaults['mail_port'], 'min' => 1, 'max' => 65535, 'dependsOn' => ['key' => 'mail_smtps', 'value' => true]],
-                ['key' => 'mail_smtpauth', 'label' => '启用 SMTPAuth', 'type' => 'switch', 'default' => $defaults['mail_smtpauth'], 'dependsOn' => ['key' => 'mail_smtps', 'value' => true]],
                 ['key' => 'mail_smtpsecure', 'label' => '加密方式', 'type' => 'select', 'default' => $defaults['mail_smtpsecure'], 'options' => [['label' => 'SSL', 'value' => 'ssl'], ['label' => 'TLS', 'value' => 'tls'], ['label' => '不加密', 'value' => '']], 'dependsOn' => ['key' => 'mail_smtps', 'value' => true]],
             ]],
             ['key' => 'branding', 'title' => '邮件品牌', 'fields' => [
diff --git a/tests/widget-system/email-system-contract.test.cjs b/tests/widget-system/email-system-contract.test.cjs
index 124033f6..571c5144 100644
--- a/tests/widget-system/email-system-contract.test.cjs
+++ b/tests/widget-system/email-system-contract.test.cjs
@@ -9,6 +9,7 @@ const read = (file) => fs.readFileSync(path.join(root, file), 'utf8')
 const templates = read('src/Settings/MailTemplates.php')
 const mail = read('src/Settings/Mail.php')
 const notifications = read('src/Settings/MailNotifications.php')
+const coreHooks = read('inc/core-hooks/part-2.php')
 const globalController = read('src/Admin/GlobalController.php')
 const userController = read('src/Admin/UserController.php')
 const settings = read('src/Settings/Settings.php')
@@ -37,11 +38,28 @@ test('email templates and SMTP use one aksrt_settings schema', () => {
   assert.match(templates, /'option_key'\s*=>\s*'aksrt_settings'/)
   assert.match(templates, /'mail_passwd'.*'secret'\s*=>\s*true/)
   assert.match(mail, /Settings::get_all\(\)/)
+  assert.match(mail, /'auth'\s*=>\s*\$username\s*!==\s*''\s*&&\s*\$password\s*!==\s*''/)
+  assert.doesNotMatch(templates, /mail_smtpauth/)
+  assert.doesNotMatch(mail, /mail_smtpauth/)
   assert.doesNotMatch(settings, /aksrt_mail_smtp/)
   assert.doesNotMatch(globalController, /aksrt_mail_config|\/settings\/mail'/)
   assert.doesNotMatch(userController, /aksrt_mail_templates|mail-templates/)
 })
 
+test('SMTP authentication and failures use the canonical mail service', () => {
+  assert.match(coreHooks, /\$phpmailer->SMTPAuth\s*=\s*!empty\(\$mail\['auth'\]\)\s*&&\s*!empty\(\$mail\['username'\]\)/)
+  assert.match(mail, /add_action\('wp_mail_failed',\s*\$capture_failure\)/)
+  assert.match(mail, /remove_action\('wp_mail_failed',\s*\$capture_failure\)/)
+  assert.match(mail, /error_log\('\[AKSRT\] SMTP 测试失败：'/)
+  assert.match(globalController, /详细原因已写入服务器错误日志/)
+})
+
+test('canonical mail service contains no obsolete catalog or placeholder branches', () => {
+  assert.doesNotMatch(mail, /public static function events\s*\(/)
+  assert.doesNotMatch(mail, /replace_placeholders\([^\n]+,\s*false\)/)
+  assert.doesNotMatch(mail, /replace_placeholders\(string \$value, array \$placeholders, bool \$html\)/)
+})
+
 test('only the canonical mail service calls wp_mail', () => {
   const phpFiles = []
   const walk = (dir) => {