diff --git a/mail/MailService.php b/mail/MailService.php
index 7183f75..a416e16 100644
--- a/mail/MailService.php
+++ b/mail/MailService.php
@@ -15,14 +15,21 @@ class MailService
         $cfg = self::loadConfig();
         $transport = strtolower((string)($cfg['transport'] ?? 'smtp'));
 
-        if ($transport === 'smtp') {
-            if (!self::ensurePHPMailerLoaded()) {
-                return [ 'success' => false, 'error' => 'PHPMailer not available for SMTP transport' ];
-            }
-            return self::sendSmtpMail($cfg, $to, $subject, $htmlBody, $textBody, $opts);
+        if ($transport !== 'smtp') {
+            return [
+                'success' => false,
+                'error' => 'MAIL_TRANSPORT must be set to smtp. Native mail() transport is disabled.',
+            ];
         }
 
-        return self::sendNativeMail($cfg, $to, $subject, $htmlBody, $textBody, $opts);
+        if (!self::ensurePHPMailerLoaded()) {
+            return [
+                'success' => false,
+                'error' => 'SMTP transport requires PHPMailer. Install it via Composer or make the system PHPMailer package available in include_path.',
+            ];
+        }
+
+        return self::sendSmtpMail($cfg, $to, $subject, $htmlBody, $textBody, $opts);
     }
 
     private static function loadConfig(): array
@@ -116,6 +123,25 @@ class MailService
         return null;
     }
 
+    private static function validateSmtpConfig(array $cfg): ?string
+    {
+        $required = [
+            'smtp_host' => 'SMTP_HOST',
+            'smtp_port' => 'SMTP_PORT',
+            'smtp_user' => 'SMTP_USER',
+            'smtp_pass' => 'SMTP_PASS',
+        ];
+
+        foreach ($required as $key => $envName) {
+            $value = $cfg[$key] ?? null;
+            if ($value === null || $value === '') {
+                return sprintf('Missing SMTP configuration: %s', $envName);
+            }
+        }
+
+        return null;
+    }
+
     private static function buildRecipientList($to): array
     {
         if ($to) {
@@ -137,6 +163,11 @@ class MailService
 
     private static function sendSmtpMail(array $cfg, $to, string $subject, string $htmlBody, ?string $textBody, array $opts): array
     {
+        $configError = self::validateSmtpConfig($cfg);
+        if ($configError !== null) {
+            return [ 'success' => false, 'error' => $configError ];
+        }
+
         $mail = new PHPMailer\PHPMailer\PHPMailer(true);
 
         try {
@@ -259,30 +290,30 @@ class MailService
             $headers[] = 'Bcc: ' . implode(', ', $bccList);
         }
 
-        $message = "--{$boundary}
+        $message = "--{$boundary}
 "
-            . "Content-Type: text/plain; charset=UTF-8
+            . "Content-Type: text/plain; charset=UTF-8
 "
-            . "Content-Transfer-Encoding: 8bit
-
+            . "Content-Transfer-Encoding: 8bit
+
 "
-            . $textBody . "
-
+            . $textBody . "
+
 "
-            . "--{$boundary}
+            . "--{$boundary}
 "
-            . "Content-Type: text/html; charset=UTF-8
+            . "Content-Type: text/html; charset=UTF-8
 "
-            . "Content-Transfer-Encoding: 8bit
-
+            . "Content-Transfer-Encoding: 8bit
+
 "
-            . $htmlBody . "
-
+            . $htmlBody . "
+
 "
-            . "--{$boundary}--
+            . "--{$boundary}--
 ";
 
-        $ok = @mail(implode(', ', $validTo), $encodedSubject, $message, implode("
+        $ok = @mail(implode(', ', $validTo), $encodedSubject, $message, implode("
 ", $headers));
         if (!$ok) {
             return [ 'success' => false, 'error' => 'Native mail() failed' ];