diff -r a8f8ada7825c Lib/smtpd.py
--- a/Lib/smtpd.py	Fri Jun 12 16:48:30 2015 -0400
+++ b/Lib/smtpd.py	Sat Jun 13 16:28:44 2015 +1200
@@ -399,10 +399,6 @@
         if not arg:
             self.push('501 Syntax: HELO hostname')
             return
-        # See issue #21783 for a discussion of this behavior.
-        if self.seen_greeting:
-            self.push('503 Duplicate HELO/EHLO')
-            return
         self._set_rset_state()
         self.seen_greeting = arg
         self.push('250 %s' % self.fqdn)
@@ -411,10 +407,6 @@
         if not arg:
             self.push('501 Syntax: EHLO hostname')
             return
-        # See issue #21783 for a discussion of this behavior.
-        if self.seen_greeting:
-            self.push('503 Duplicate HELO/EHLO')
-            return
         self._set_rset_state()
         self.seen_greeting = arg
         self.extended_smtp = True
diff -r a8f8ada7825c Lib/test/test_smtpd.py
--- a/Lib/test/test_smtpd.py	Fri Jun 12 16:48:30 2015 -0400
+++ b/Lib/test/test_smtpd.py	Sat Jun 13 16:28:44 2015 +1200
@@ -333,14 +333,15 @@
     def test_EHLO_duplicate(self):
         self.write_line(b'EHLO example')
         self.write_line(b'EHLO example')
-        self.assertEqual(self.channel.socket.last,
-                         b'503 Duplicate HELO/EHLO\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 HELP\r\n')
 
     def test_EHLO_HELO_duplicate(self):
+        name = smtpd.socket.getfqdn()
         self.write_line(b'EHLO example')
+        self.assertEqual(self.channel.socket.last, b'250 HELP\r\n')
         self.write_line(b'HELO example')
         self.assertEqual(self.channel.socket.last,
-                         b'503 Duplicate HELO/EHLO\r\n')
+                         '250 {}\r\n'.format(name).encode('ascii'))
 
     def test_HELO(self):
         name = smtpd.socket.getfqdn()
@@ -351,8 +352,7 @@
     def test_HELO_EHLO_duplicate(self):
         self.write_line(b'HELO example')
         self.write_line(b'EHLO example')
-        self.assertEqual(self.channel.socket.last,
-                         b'503 Duplicate HELO/EHLO\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 HELP\r\n')
 
     def test_HELP(self):
         self.write_line(b'HELP')
@@ -377,10 +377,11 @@
                          b'501 Syntax: HELO hostname\r\n')
 
     def test_HELO_duplicate(self):
+        name = smtpd.socket.getfqdn()
         self.write_line(b'HELO example')
         self.write_line(b'HELO example')
         self.assertEqual(self.channel.socket.last,
-                         b'503 Duplicate HELO/EHLO\r\n')
+                         '250 {}\r\n'.format(name).encode('ascii'))
 
     def test_HELO_parameter_rejected_when_extensions_not_enabled(self):
         self.extended_smtp = False