--- a/Lib/test/test_smtpd.py
+++ b/Lib/test/test_smtpd.py
@@ -1,4 +1,4 @@
-from unittest import TestCase
+import unittest
 from test import support, mock_socket
 import socket
 import io
@@ -26,7 +26,7 @@
         raise DummyDispatcherBroken()
 
 
-class SMTPDServerTest(TestCase):
+class SMTPDServerTest(unittest.TestCase):
     def setUp(self):
         smtpd.socket = asyncore.socket = mock_socket
 
@@ -49,7 +49,7 @@
         asyncore.socket = smtpd.socket = socket
 
 
-class SMTPDChannelTest(TestCase):
+class SMTPDChannelTest(unittest.TestCase):
     def setUp(self):
         smtpd.socket = asyncore.socket = mock_socket
         self.old_debugstream = smtpd.DEBUGSTREAM
@@ -78,10 +78,26 @@
         self.assertEqual(self.channel.socket.last,
                          b'500 Error: bad syntax\r\n')
 
-    def test_EHLO_not_implemented(self):
+    def test_EHLO(self):
+        self.write_line(b'EHLO test.example')
+        self.assertEqual(self.channel.socket.last, b'250 HELP\r\n')
+
+    def test_EHLO_bad_syntax(self):
+        self.write_line(b'EHLO')
+        self.assertEqual(self.channel.socket.last,
+                         b'501 Syntax: EHLO hostname\r\n')
+
+    def test_EHLO_duplicate(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'EHLO test.example')
         self.assertEqual(self.channel.socket.last,
-                         b'502 Error: command "EHLO" not implemented\r\n')
+                         b'503 Duplicate HELO/EHLO\r\n')
+
+    def test_EHLO_HELO_duplicate(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'HELO test.example')
+        self.assertEqual(self.channel.socket.last,
+                         b'503 Duplicate HELO/EHLO\r\n')
 
     def test_HELO(self):
         name = smtpd.socket.getfqdn()
@@ -89,6 +105,29 @@
         self.assertEqual(self.channel.socket.last,
                          '250 {}\r\n'.format(name).encode('ascii'))
 
+    def test_HELO_EHLO_duplicate(self):
+        self.write_line(b'HELO test.example')
+        self.write_line(b'EHLO test.example')
+        self.assertEqual(self.channel.socket.last,
+                         b'503 Duplicate HELO/EHLO\r\n')
+
+    def test_HELP(self):
+        self.write_line(b'HELP')
+        self.assertEqual(self.channel.socket.last,
+                         b'250 Supported commands: EHLO HELO MAIL RCPT ' + \
+                         b'DATA RSET NOOP QUIT VRFY\r\n')
+
+    def test_HELP_command(self):
+        self.write_line(b'HELP MAIL')
+        self.assertEqual(self.channel.socket.last,
+                         b'250 Syntax: MAIL FROM:<address>\r\n')
+
+    def test_HELP_command_unknown(self):
+        self.write_line(b'HELP SPAM')
+        self.assertEqual(self.channel.socket.last,
+                         b'501 Supported commands: EHLO HELO MAIL RCPT ' + \
+                         b'DATA RSET NOOP QUIT VRFY\r\n')
+
     def test_HELO_bad_syntax(self):
         self.write_line(b'HELO')
         self.assertEqual(self.channel.socket.last,
@@ -100,9 +139,33 @@
         self.assertEqual(self.channel.socket.last,
                          b'503 Duplicate HELO/EHLO\r\n')
 
+    def test_HELO_extensions_not_enabled(self):
+        self.extended_smtp = False
+        self.write_line(b'HELO test.example')
+        self.write_line(b'MAIL from:<foo@example.com> SIZE=1234')
+        self.assertEqual(self.channel.socket.last,
+                         b'501 Syntax: MAIL FROM:<address>\r\n')
+
+    def test_no_HELO_EHLO_defaults_to_HELO(self):
+        self.write_line(b'MAIL FROM:<eggs@example> SIZE=10')
+        self.assertEqual(self.channel.socket.last,
+                         b'501 Syntax: MAIL FROM:<address>\r\n')
+
+    def test_MAIL_allows_space_after_colon(self):
+        self.write_line(b'HELO test.example')
+        self.write_line(b'MAIL from:   <foo@example.com>')
+        self.assertEqual(self.channel.socket.last,
+                         b'250 OK\r\n')
+
+    def test_extended_MAIL_allows_space_after_colon(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL from:   <foo@example.com> size=20')
+        self.assertEqual(self.channel.socket.last,
+                         b'250 OK\r\n')
+
     def test_NOOP(self):
         self.write_line(b'NOOP')
-        self.assertEqual(self.channel.socket.last, b'250 Ok\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
 
     def test_NOOP_bad_syntax(self):
         self.write_line(b'NOOP hi')
@@ -124,15 +187,30 @@
                          b'451 Internal confusion\r\n')
 
     def test_command_too_long(self):
-        self.write_line(b'MAIL from ' +
+        self.write_line(b'HELO test.example')
+        self.write_line(b'MAIL from:<' +
                         b'a' * self.channel.command_size_limit +
-                        b'@example')
+                        b'@example>')
         self.assertEqual(self.channel.socket.last,
                          b'500 Error: line too long\r\n')
 
-    def test_data_too_long(self):
-        # Small hack. Setting limit to 2K octets here will save us some time.
-        self.channel.data_size_limit = 2048
+    def test_MAIL_command_limit_extended_with_SIZE(self):
+        self.write_line(b'EHLO test.example')
+        fill_len = self.channel.command_size_limit - len('MAIL from:<@example>')
+        self.write_line(b'MAIL from:<' +
+                        b'a' * fill_len +
+                        b'@example> SIZE=1234')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+
+        self.write_line(b'MAIL from:<' +
+                        b'a' * (fill_len + 26) +
+                        b'@example> SIZE=1234')
+        self.assertEqual(self.channel.socket.last,
+                         b'500 Error: line too long\r\n')
+
+    def test_data_longer_than_default_data_size_limit(self):
+        # Hack the default so we don't have to generate so much data.
+        self.channel.data_size_limit = 1048
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT To:spam@example')
         self.write_line(b'DATA')
@@ -141,64 +219,146 @@
         self.assertEqual(self.channel.socket.last,
                          b'552 Error: Too much mail data\r\n')
 
+    def test_MAIL_ok_without_HELO_EHLO(self):
+        # This actually violates the RFC, but we haven't historically
+        # enforced this, and old mail servers didn't either.
+        self.write_line(b'MAIL FROM:<eggs@example>')
+        self.assertEqual(self.channel.socket.last,
+                         b'250 OK\r\n')
+
+    def test_MAIL_size_parameter(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL FROM:<eggs@example> SIZE=512')
+        self.assertEqual(self.channel.socket.last,
+                         b'250 OK\r\n')
+
+    def test_MAIL_invalid_size_parameter(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL FROM:<eggs@example> SIZE=invalid')
+        self.assertEqual(self.channel.socket.last,
+            b'501 Syntax: MAIL FROM:<address> [SP <mail-parameters>]\r\n')
+
+    def test_MAIL_RCPT_unknown_parameters(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL FROM:<eggs@example> ham=green')
+        self.assertEqual(self.channel.socket.last,
+            b'555 MAIL FROM parameters not recognized or not implemented\r\n')
+
+        self.write_line(b'MAIL FROM:<eggs@example>')
+        self.write_line(b'RCPT TO:<eggs@example> ham=green')
+        self.assertEqual(self.channel.socket.last,
+            b'555 RCPT TO parameters not recognized or not implemented\r\n')
+
+    def test_MAIL_size_parameter_larger_than_default_data_size_limit(self):
+        self.channel.data_size_limit = 1048
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL FROM:<eggs@example> SIZE=2096')
+        self.assertEqual(self.channel.socket.last,
+            b'552 Error: message size exceeds fixed maximum message size\r\n')
+
     def test_need_MAIL(self):
         self.write_line(b'RCPT to:spam@example')
         self.assertEqual(self.channel.socket.last,
             b'503 Error: need MAIL command\r\n')
 
     def test_MAIL_syntax(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL from eggs@example')
         self.assertEqual(self.channel.socket.last,
-            b'501 Syntax: MAIL FROM:<address>\r\n')
+            b'501 Syntax: MAIL FROM:<address> [SP <mail-parameters>]\r\n')
 
     def test_MAIL_missing_from(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL from:')
         self.assertEqual(self.channel.socket.last,
-            b'501 Syntax: MAIL FROM:<address>\r\n')
+            b'501 Syntax: MAIL FROM:<address> [SP <mail-parameters>]\r\n')
 
     def test_MAIL_chevrons(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL from:<eggs@example>')
-        self.assertEqual(self.channel.socket.last, b'250 Ok\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+
+    def test_MAIL_empty_chevrons(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL from:<>')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+
+    # Parsing of quoted localpart of email addresses requires a full parser
+    # implementation, and will need to wait for email 6 package.  See RFC 3696
+    # for valid addresses the server needs to be able to parse.
+    @unittest.expectedFailure
+    def test_MAIL_quoted_localpart(self):
+        self.write_line(b'EHLO test.example')
+        self.write_line(b'MAIL from:<"Fred Blogs"@example.com>')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+        self.write_line(b'RSET')
+        self.write_line(b'MAIL from:<Abc\>def@example.com>')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
 
     def test_nested_MAIL(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL from:eggs@example')
         self.write_line(b'MAIL from:spam@example')
         self.assertEqual(self.channel.socket.last,
             b'503 Error: nested MAIL command\r\n')
 
+    def test_VRFY(self):
+        self.write_line(b'VRFY eggs@example')
+        self.assertEqual(self.channel.socket.last,
+            b'252 Cannot VRFY user, but will accept message and attempt ' + \
+            b'delivery\r\n')
+
+    def test_VRFY_syntax(self):
+        self.write_line(b'VRFY')
+        self.assertEqual(self.channel.socket.last,
+            b'501 Syntax: VRFY <address>\r\n')
+
+    def test_EXPN_not_implemented(self):
+        self.write_line(b'EXPN')
+        self.assertEqual(self.channel.socket.last,
+            b'502 EXPN not implemented\r\n')
+
     def test_need_RCPT(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'DATA')
         self.assertEqual(self.channel.socket.last,
             b'503 Error: need RCPT command\r\n')
 
     def test_RCPT_syntax(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT to eggs@example')
         self.assertEqual(self.channel.socket.last,
-            b'501 Syntax: RCPT TO: <address>\r\n')
+            b'501 Syntax: RCPT TO:<address> [SP <mail-parameters>]\r\n')
+
+        self.write_line(b'RCPT to:<eggs@example>')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
 
     def test_data_dialog(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
-        self.assertEqual(self.channel.socket.last, b'250 Ok\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
         self.write_line(b'RCPT To:spam@example')
-        self.assertEqual(self.channel.socket.last, b'250 Ok\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
 
         self.write_line(b'DATA')
         self.assertEqual(self.channel.socket.last,
             b'354 End data with <CR><LF>.<CR><LF>\r\n')
         self.write_line(b'data\r\nmore\r\n.')
-        self.assertEqual(self.channel.socket.last, b'250 Ok\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
         self.assertEqual(self.server.messages,
             [('peer', 'eggs@example', ['spam@example'], 'data\nmore')])
 
     def test_DATA_syntax(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT To:spam@example')
         self.write_line(b'DATA spam')
         self.assertEqual(self.channel.socket.last, b'501 Syntax: DATA\r\n')
 
     def test_data_transparency_section_4_5_2(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT To:spam@example')
         self.write_line(b'DATA')
@@ -206,6 +366,7 @@
         self.assertEqual(self.channel.received_data, '.')
 
     def test_multiple_RCPT(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT To:spam@example')
         self.write_line(b'RCPT To:ham@example')
@@ -216,6 +377,7 @@
 
     def test_manual_status(self):
         # checks that the Channel is able to return a custom status message
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT To:spam@example')
         self.write_line(b'DATA')
@@ -223,10 +385,11 @@
         self.assertEqual(self.channel.socket.last, b'250 Okish\r\n')
 
     def test_RSET(self):
+        self.write_line(b'EHLO test.example')
         self.write_line(b'MAIL From:eggs@example')
         self.write_line(b'RCPT To:spam@example')
         self.write_line(b'RSET')
-        self.assertEqual(self.channel.socket.last, b'250 Ok\r\n')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
         self.write_line(b'MAIL From:foo@example')
         self.write_line(b'RCPT To:eggs@example')
         self.write_line(b'DATA')
@@ -238,6 +401,12 @@
         self.write_line(b'RSET hi')
         self.assertEqual(self.channel.socket.last, b'501 Syntax: RSET\r\n')
 
+    def test_unknown_command(self):
+        self.write_line(b'UNKNOWN_CMD')
+        self.assertEqual(self.channel.socket.last,
+                         b'500 Error: command "UNKNOWN_CMD" not ' + \
+                         b'recognized\r\n')
+
     def test_attribute_deprecations(self):
         with support.check_warnings(('', DeprecationWarning)):
             spam = self.channel._SMTPChannel__server
@@ -284,8 +453,55 @@
         with support.check_warnings(('', DeprecationWarning)):
             self.channel._SMTPChannel__addr = 'spam'
 
+
+class SMTPDChannelWithDataSizeLimitTest(unittest.TestCase):
+
+    def setUp(self):
+        smtpd.socket = asyncore.socket = mock_socket
+        self.debug = smtpd.DEBUGSTREAM = io.StringIO()
+        self.server = DummyServer('a', 'b')
+        conn, addr = self.server.accept()
+        # Set DATA size limit to 32 bytes for easy testing
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr, 32)
+
+    def tearDown(self):
+        asyncore.socket = smtpd.socket = socket
+
+    def write_line(self, line):
+        self.channel.socket.queue_recv(line)
+        self.channel.handle_read()
+
+    def test_data_limit_dialog(self):
+        self.write_line(b'MAIL From:eggs@example')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+        self.write_line(b'RCPT To:spam@example')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+
+        self.write_line(b'DATA')
+        self.assertEqual(self.channel.socket.last,
+            b'354 End data with <CR><LF>.<CR><LF>\r\n')
+        self.write_line(b'data\r\nmore\r\n.')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+        self.assertEqual(self.server.messages,
+            [('peer', 'eggs@example', ['spam@example'], 'data\nmore')])
+
+    def test_data_limit_dialog_too_much_data(self):
+        self.write_line(b'MAIL From:eggs@example')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+        self.write_line(b'RCPT To:spam@example')
+        self.assertEqual(self.channel.socket.last, b'250 OK\r\n')
+
+        self.write_line(b'DATA')
+        self.assertEqual(self.channel.socket.last,
+            b'354 End data with <CR><LF>.<CR><LF>\r\n')
+        self.write_line(b'This message is longer than 32 bytes\r\n.')
+        self.assertEqual(self.channel.socket.last,
+                         b'552 Error: Too much mail data\r\n')
+
+
 def test_main():
-    support.run_unittest(SMTPDServerTest, SMTPDChannelTest)
+    support.run_unittest(SMTPDServerTest, SMTPDChannelTest,
+                         SMTPDChannelWithDataSizeLimitTest)
 
 if __name__ == "__main__":
     test_main()