diff --git a/Lib/smtplib.py b/Lib/smtplib.py
index a634f7a..8e3d4bf 100755
--- a/Lib/smtplib.py
+++ b/Lib/smtplib.py
@@ -54,7 +54,7 @@
 import sys
 from email.base64mime import body_encode as encode_base64
 
-__all__ = ["SMTPException", "SMTPServerDisconnected", "SMTPResponseException",
+__all__ = ["SMTPException", "SMTPNotSupportedError", "SMTPServerDisconnected", "SMTPResponseException",
            "SMTPSenderRefused", "SMTPRecipientsRefused", "SMTPDataError",
            "SMTPConnectError", "SMTPHeloError", "SMTPAuthenticationError",
            "quoteaddr", "quotedata", "SMTP"]