diff -r c47a72627f0c Doc/library/smtplib.rst
--- a/Doc/library/smtplib.rst	Sun Jan 22 14:41:42 2017 +0800
+++ b/Doc/library/smtplib.rst	Sun Jan 22 23:31:20 2017 -0500
@@ -499,7 +499,8 @@
    :mailheader:`Cc`, and :mailheader:`Bcc` fields from *msg*.  If exactly one
    set of :mailheader:`Resent-*` headers appear in the message, the regular
    headers are ignored and the :mailheader:`Resent-*` headers are used instead.
-   If the message contains more than one set of :mailheader:`Resent-*` headers,
+   If the message contains more than one set of :mailheader:`Resent-*` headers
+   in the same block (not separated by traces or other headers),
    a :exc:`ValueError` is raised, since there is no way to unambiguously detect
    the most recent set of :mailheader:`Resent-` headers.
 
diff -r c47a72627f0c Lib/smtplib.py
--- a/Lib/smtplib.py	Sun Jan 22 14:41:42 2017 +0800
+++ b/Lib/smtplib.py	Sun Jan 22 23:31:20 2017 -0500
@@ -914,28 +914,30 @@
         # if there is more than one 'Resent-' block there's no way to
         # unambiguously determine which one is the most recent in all cases,
         # so rather than guess we raise a ValueError in that case.
-        #
-        # TODO implement heuristics to guess the correct Resent-* block with an
-        # option allowing the user to enable the heuristics.  (It should be
-        # possible to guess correctly almost all of the time.)
 
-        self.ehlo_or_helo_if_needed()
-        resent = msg.get_all('Resent-Date')
-        if resent is None:
-            header_prefix = ''
-        elif len(resent) == 1:
-            header_prefix = 'Resent-'
-        else:
-            raise ValueError("message has more than one 'Resent-' header block")
+        #Resent or Original? (get the first resent-block)
+        resent_block = []
+        for header in msg._headers:
+            if header[0].startswith('Resent'):
+                resent_block.append(header)
+            elif resent_block:
+                break
+
+        if [header[0] for header in resent_block].count('Resent-Date') > 1:
+           raise ValueError("message has more than one 'Resent-Date' in same header block")
+        
+        header_prefix = 'Resent-' if len(resent_block) >= 1 else ''
+        headers_to_consider = dict(resent_block) if len(resent_block) >= 1 else msg
+            
         if from_addr is None:
             # Prefer the sender field per RFC 2822:3.6.2.
             from_addr = (msg[header_prefix + 'Sender']
-                           if (header_prefix + 'Sender') in msg
+                           if (header_prefix + 'Sender') in headers_to_consider
                            else msg[header_prefix + 'From'])
         if to_addrs is None:
-            addr_fields = [f for f in (msg[header_prefix + 'To'],
-                                       msg[header_prefix + 'Bcc'],
-                                       msg[header_prefix + 'Cc'])
+            addr_fields = [f for f in (headers_to_consider.get(header_prefix + 'To',None),
+                                       headers_to_consider.get(header_prefix + 'Bcc',None),
+                                       headers_to_consider.get(header_prefix + 'Cc',None))
                            if f is not None]
             to_addrs = [a[1] for a in email.utils.getaddresses(addr_fields)]
         # Make a local copy so we can delete the bcc headers.
diff -r c47a72627f0c Lib/test/test_smtplib.py
--- a/Lib/test/test_smtplib.py	Sun Jan 22 14:41:42 2017 +0800
+++ b/Lib/test/test_smtplib.py	Sun Jan 22 23:31:20 2017 -0500
@@ -531,7 +531,7 @@
                                  re.MULTILINE)
             self.assertRegex(debugout, to_addr)
 
-    def testSendMessageMultipleResentRaises(self):
+    def testSendMessageMultipleResentInSameBlockRaises(self):
         m = email.mime.text.MIMEText('A test message')
         m['From'] = 'foo@bar.com'
         m['To'] = 'John'
@@ -549,6 +549,43 @@
             smtp.send_message(m)
         smtp.close()
 
+    def testSendMessageMultipleResentBlock(self):
+        first_date = 'Thu, 1 Jan 1970 17:42:00 +0000'
+        first_from = 'holy@grail.net'
+        first_to  = 'Martha <my_mom@great.cooker.com>, Jeff'
+        m = email.mime.text.MIMEText('A test message')
+        m['From'] = 'foo@bar.com'
+        m['To'] = 'John'
+        m['CC'] = 'Sally, Fred'
+        m['Bcc'] = 'John Root <root@localhost>, "Dinsdale" <warped@silly.walks.com>'
+        m['Resent-Bcc'] = 'doe@losthope.net'
+        m['Resent-Date'] = 'Thu, 2 Jan 1970 17:42:00 +0000'
+        m['Resent-To'] = 'holy@grail.net'
+        m['Resent-From'] = 'Martha <my_mom@great.cooker.com>, Jeff'
+        # a message should have Resent headers block separated by Return-paths and traces
+        m._headers.insert(0,m.policy.header_store_parse('Return-Path', 'holy@grail.net'))
+        # this prepend to the "list" in email message class
+        m._headers.insert(0,m.policy.header_store_parse('Resent-Date', first_date))
+        m._headers.insert(0,m.policy.header_store_parse('Resent-From', first_from))
+        m._headers.insert(0,m.policy.header_store_parse('Resent-To', first_to))
+
+        smtp = smtplib.SMTP(HOST, self.port, local_hostname='localhost', timeout=3)
+        smtp.send_message(m)
+        self.assertEqual(first=m.get('Resent-Date'),
+                         second=first_date,
+                         msg="""
+                             The Resent-Date order is not read correctly or
+                             something wrong happened.
+                             """)
+        self.assertEqual(first=m.get('Resent-From'),
+                         second=first_from,
+                         msg="""
+                             The Resent-From order is not read correctly or
+                             something wrong happened.
+                             """)
+        smtp.close()
+
+
 class NonConnectingTests(unittest.TestCase):
 
     def testNotConnected(self):