diff --git a/Lib/smtpd.py b/Lib/smtpd.py
index 5f3b05e..8103ca9 100755
--- a/Lib/smtpd.py
+++ b/Lib/smtpd.py
@@ -89,7 +89,10 @@
 from warnings import warn
 from email._header_value_parser import get_addr_spec, get_angle_addr
 
-__all__ = ["SMTPServer","DebuggingServer","PureProxy","MailmanProxy"]
+__all__ = [
+    "SMTPChannel", "SMTPServer", "DebuggingServer", "PureProxy",
+    "MailmanProxy",
+]
 
 program = sys.argv[0]
 __version__ = 'Python SMTP proxy version 0.3'
diff --git a/Lib/test/test_smtpd.py b/Lib/test/test_smtpd.py
index d92c9b3..3eebe94 100644
--- a/Lib/test/test_smtpd.py
+++ b/Lib/test/test_smtpd.py
@@ -998,5 +998,16 @@
             self.write_line(b'test\r\n.')
             self.assertEqual(self.channel.socket.last[0:3], b'250')
 
+
+class MiscTestCase(unittest.TestCase):
+    def test__all__(self):
+        blacklist = {
+            "program", "Devnull", "DEBUGSTREAM", "NEWLINE", "COMMASPACE",
+            "DATA_SIZE_DEFAULT", "usage", "Options", "parseargs",
+
+        }
+        support.check__all__(self, smtpd, blacklist=blacklist)
+
+
 if __name__ == "__main__":
     unittest.main()