Added SMTP PLAIN authentication method

Author: ip-qi

system/Email/Email.php

@@ -279,6 +279,13 @@ class Email
      */
     protected $SMTPAuth = false;
 
+    /**
+     * Which SMTP atuh method to use ('LOGIN', 'PLAIN')
+     *
+     * @var bool
+     */
+    protected $SMTPAuthMethod = 'LOGIN';
+
     /**
      * Whether to send a Reply-To header
      *
@@ -1920,9 +1927,9 @@ protected function SMTPConnect()
                 $this->SMTPConnect,
                 true,
                 STREAM_CRYPTO_METHOD_TLSv1_0_CLIENT
-                | STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT
-                | STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT
-                | STREAM_CRYPTO_METHOD_TLSv1_3_CLIENT,
+                    | STREAM_CRYPTO_METHOD_TLSv1_1_CLIENT
+                    | STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT
+                    | STREAM_CRYPTO_METHOD_TLSv1_3_CLIENT,
             );
 
             if ($crypto !== true) {
@@ -2015,49 +2022,72 @@ protected function sendCommand($cmd, $data = '')
      */
     protected function SMTPAuthenticate()
     {
-        if (! $this->SMTPAuth) {
+        if (!$this->SMTPAuth) {
             return true;
         }
 
-        if ($this->SMTPUser === '' && $this->SMTPPass === '') {
+        // If no username or password is set
+        if ($this->SMTPUser === '' || $this->SMTPPass === '') {
             $this->setErrorMessage(lang('Email.noSMTPAuth'));
 
             return false;
         }
 
-        $this->sendData('AUTH LOGIN');
-        $reply = $this->getSMTPData();
+        switch ($this->SMTPAuthMethod) {
+            case 'LOGIN':
+                $this->sendData('AUTH LOGIN');
+                $reply = $this->getSMTPData();
 
-        if (str_starts_with($reply, '503')) {    // Already authenticated
-            return true;
-        }
+                if (str_starts_with($reply, '503')) {    // Already authenticated
+                    return true;
+                }
 
-        if (! str_starts_with($reply, '334')) {
-            $this->setErrorMessage(lang('Email.failedSMTPLogin', [$reply]));
+                if (! str_starts_with($reply, '334')) {
+                    $this->setErrorMessage(lang('Email.failedSMTPLogin', [$reply]));
 
-            return false;
-        }
+                    return false;
+                }
 
-        $this->sendData(base64_encode($this->SMTPUser));
-        $reply = $this->getSMTPData();
+                $this->sendData(base64_encode($this->SMTPUser));
+                $reply = $this->getSMTPData();
 
-        if (! str_starts_with($reply, '334')) {
-            $this->setErrorMessage(lang('Email.SMTPAuthUsername', [$reply]));
+                if (! str_starts_with($reply, '334')) {
+                    $this->setErrorMessage(lang('Email.SMTPAuthUsername', [$reply]));
 
-            return false;
-        }
+                    return false;
+                }
 
-        $this->sendData(base64_encode($this->SMTPPass));
-        $reply = $this->getSMTPData();
+                $this->sendData(base64_encode($this->SMTPPass));
+                $reply = $this->getSMTPData();
 
-        if (! str_starts_with($reply, '235')) {
-            $this->setErrorMessage(lang('Email.SMTPAuthPassword', [$reply]));
+                if (!str_starts_with($reply, '235')) {
+                    $this->setErrorMessage(lang('Email.SMTPAuthPassword', [$reply]));
 
-            return false;
+                    return false;
+                }
+                break;
+            case 'PLAIN':
+                // Generate single command for PLAIN authentication
+                $authString = "\0" . $this->SMTPUser . "\0" . $this->SMTPPass;
+
+                $this->sendData('AUTH PLAIN ' . base64_encode($authString));
+                $reply = $this->getSMTPData();
+
+                if (! str_starts_with($reply, '235') || ! str_starts_with($reply, '503')) {
+                    $this->setErrorMessage(lang('Email.failedSMTPLogin', [$reply]));
+
+                    return false;
+                }
+
+                break;
+            default:
+                $this->setErrorMessage(lang('Email.noSMTPAuthMethod'));
+
+                return false;
         }
 
         if ($this->SMTPKeepAlive) {
-            $this->SMTPAuth = false;
+            $this->SMTPAuth = false; // Prevent re-authentication for keep-alive sessions
         }
 
         return true;

system/Language/en/Email.php

@@ -27,6 +27,7 @@
     'noHostname'           => 'You did not specify a SMTP hostname.',
     'SMTPError'            => 'The following SMTP error was encountered: {0}',
     'noSMTPAuth'           => 'Error: You must assign an SMTP username and password.',
+    'noSMTPAuthMethod'     => 'Error: you must assign an SMTP authentication method ("LOGIN" or "PLAIN")',
     'failedSMTPLogin'      => 'Failed to send AUTH LOGIN command. Error: {0}',
     'SMTPAuthUsername'     => 'Failed to authenticate username. Error: {0}',
     'SMTPAuthPassword'     => 'Failed to authenticate password. Error: {0}',