diff -r b49e366556ba Lib/smtplib.py
--- a/Lib/smtplib.py	Mon Jun 02 14:43:24 2014 +0200
+++ b/Lib/smtplib.py	Mon Jun 02 17:53:56 2014 +0300
@@ -377,6 +377,7 @@
             if self.debuglevel > 0:
                 print('reply:', repr(line), file=stderr)
             if len(line) > _MAXLINE:
+                self.close()
                 raise SMTPResponseException(500, "Line too long.")
             resp.append(line[4:].strip(b' \t\r\n'))
             code = line[:3]