diff --git a/src/App/Mailer.php b/src/App/Mailer.php
index 91cfc91..9397554 100644
--- a/src/App/Mailer.php
+++ b/src/App/Mailer.php
@@ -193,51 +193,131 @@ final class Mailer
         stream_set_timeout($fp, 15);
 
         $transcript = [];
-        $read = function (string $label = 'read') use ($fp, &$transcript) {
-            $line = fgets($fp, 515);
-            if ($line !== false) {
-                $transcript[] = $label . ': ' . trim($line);
+        $readResponse = function (array $expectCodes = [], string $label = 'read') use ($fp, &$transcript): array {
+            $lines = [];
+            while (($line = fgets($fp, 515)) !== false) {
+                $line = rtrim($line, "\r\n");
+                $lines[] = $line;
+                $transcript[] = $label . ': ' . $line;
+                // SMTP multiline: code + '-' means more lines, code + ' ' means end
+                if (strlen($line) >= 4 && $line[3] === ' ') {
+                    break;
+                }
             }
-            return $line;
+            $code = 0;
+            if ($lines) {
+                $code = (int)substr($lines[0], 0, 3);
+            }
+            return [
+                'ok'    => !$expectCodes || in_array($code, $expectCodes, true),
+                'code'  => $code,
+                'lines' => $lines,
+            ];
         };
-        $write = function (string $cmd, string $label = 'write', bool $mask = false) use ($fp, &$transcript) {
+        $write = function (string $cmd, string $label = 'write', bool $mask = false) use ($fp, &$transcript): void {
             $transcript[] = $label . ': ' . ($mask ? '[omitted]' : $cmd);
             fwrite($fp, $cmd . "\r\n");
         };
 
-        $read();
+        $resp = $readResponse([220], 'greeting');
+        if (!$resp['ok']) {
+            fclose($fp);
+            $this->log('mail_smtp_greeting_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+            $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+            $this->sendMailFn($to, $subject, $html, $from, $fromName);
+            return;
+        }
+
         $write('EHLO ' . $this->app->config()->primaryDomain);
-        $read();
+        $resp = $readResponse([250], 'ehlo');
+        if (!$resp['ok']) {
+            fclose($fp);
+            $this->log('mail_smtp_ehlo_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+            $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+            $this->sendMailFn($to, $subject, $html, $from, $fromName);
+            return;
+        }
 
         if ($secure === 'tls') {
             $write('STARTTLS');
-            $read();
-            if (!stream_socket_enable_crypto($fp, true, STREAM_CRYPTO_METHOD_TLS_CLIENT)) {
+            $resp = $readResponse([220], 'starttls');
+            if (!$resp['ok'] || !stream_socket_enable_crypto($fp, true, STREAM_CRYPTO_METHOD_TLS_CLIENT)) {
                 fclose($fp);
-                $this->log('mail_smtp_starttls_failed', ['host' => $host, 'port' => $port]);
+                $this->log('mail_smtp_starttls_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
                 $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
                 $this->sendMailFn($to, $subject, $html, $from, $fromName);
                 return;
             }
             $write('EHLO ' . $this->app->config()->primaryDomain);
-            $read();
+            $resp = $readResponse([250], 'ehlo-tls');
+            if (!$resp['ok']) {
+                fclose($fp);
+                $this->log('mail_smtp_ehlo_tls_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+                $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+                $this->sendMailFn($to, $subject, $html, $from, $fromName);
+                return;
+            }
         }
 
         if ($user !== '') {
             $write('AUTH LOGIN');
-            $read();
+            $resp = $readResponse([334], 'auth-login');
+            if (!$resp['ok']) {
+                fclose($fp);
+                $this->log('mail_smtp_auth_login_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+                $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+                $this->sendMailFn($to, $subject, $html, $from, $fromName);
+                return;
+            }
             $write(base64_encode($user), 'auth-user', true);
-            $read();
+            $resp = $readResponse([334], 'auth-user');
+            if (!$resp['ok']) {
+                fclose($fp);
+                $this->log('mail_smtp_auth_user_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+                $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+                $this->sendMailFn($to, $subject, $html, $from, $fromName);
+                return;
+            }
             $write(base64_encode($pass), 'auth-pass', true);
-            $read();
+            $resp = $readResponse([235], 'auth-pass');
+            if (!$resp['ok']) {
+                fclose($fp);
+                $this->log('mail_smtp_auth_pass_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+                $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+                $this->sendMailFn($to, $subject, $html, $from, $fromName);
+                return;
+            }
         }
 
         $write('MAIL FROM: <' . $from . '>');
-        $read();
+        $resp = $readResponse([250], 'mail-from');
+        if (!$resp['ok']) {
+            fclose($fp);
+            $this->log('mail_smtp_mailfrom_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+            $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+            $this->sendMailFn($to, $subject, $html, $from, $fromName);
+            return;
+        }
+
         $write('RCPT TO: <' . $to . '>');
-        $read();
+        $resp = $readResponse([250, 251], 'rcpt-to');
+        if (!$resp['ok']) {
+            fclose($fp);
+            $this->log('mail_smtp_rcpt_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+            $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+            $this->sendMailFn($to, $subject, $html, $from, $fromName);
+            return;
+        }
+
         $write('DATA');
-        $read();
+        $resp = $readResponse([354], 'data-start');
+        if (!$resp['ok']) {
+            fclose($fp);
+            $this->log('mail_smtp_data_start_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
+            $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
+            $this->sendMailFn($to, $subject, $html, $from, $fromName);
+            return;
+        }
 
         $msg = "From: {$fromName} <{$from}>\r\n";
         $msg .= "To: <{$to}>\r\n";
@@ -245,14 +325,16 @@ final class Mailer
         $msg .= "MIME-Version: 1.0\r\n";
         $msg .= "Content-Type: text/html; charset=utf-8\r\n\r\n";
         $msg .= $html . "\r\n.\r\n";
-        $write($msg, 'data');
-        $resp = $read('data-response');
+        $write($msg, 'data', false);
+        $resp = $readResponse([250], 'data-end');
+
         $write('QUIT');
+        $readResponse([221], 'quit');
         fclose($fp);
 
         $this->log('mail_smtp_transcript', ['host' => $host, 'port' => $port, 'secure' => $secure, 'steps' => $transcript]);
 
-        if ($resp === false || !str_starts_with((string)$resp, '250')) {
+        if (!$resp['ok']) {
             $this->log('mail_smtp_send_failed', ['host' => $host, 'port' => $port, 'resp' => $resp]);
             $this->sendMailFn($to, $subject, $html, $from, $fromName);
             return;