diff --git a/changelog.md b/changelog.md
index d765948b..9996d4a6 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,8 @@
 # PHPMailer Change Log
 
+## WIP
+* Handle early connection errors such as 421
+
 ## Version 6.2.0
 * PHP 8.0 compatibility, many thanks to @jrf_nl!
 * Switch from PHP CS Fixer to PHP CodeSniffer for coding standards
diff --git a/src/SMTP.php b/src/SMTP.php
index ab7f46e4..0243501f 100644
--- a/src/SMTP.php
+++ b/src/SMTP.php
@@ -343,8 +343,20 @@ class SMTP
         // Get any announcement
         $this->last_reply = $this->get_lines();
         $this->edebug('SERVER -> CLIENT: ' . $this->last_reply, self::DEBUG_SERVER);
-
-        return true;
+        $responseCode = (int)substr($this->last_reply, 0, 3);
+        if ($responseCode === 220) {
+            return true;
+        }
+        //Anything other than a 220 response means something went wrong
+        //RFC 5321 says the server will wait for us to send a QUIT in response to a 554 error
+        //https://tools.ietf.org/html/rfc5321#section-3.1
+        if ($responseCode === 554) {
+            $this->quit();
+        }
+        //This will handle 421 responses which may not wait for a QUIT (e.g. if the server is being shut down)
+        $this->edebug('Connection: closing due to error', self::DEBUG_CONNECTION);
+        $this->close();
+        return false;
     }
 
     /**