diff --git a/Lib/smtpd.py b/Lib/smtpd.py
index 1fa157a..569b42e 100755
--- a/Lib/smtpd.py
+++ b/Lib/smtpd.py
@@ -98,7 +98,6 @@
 
 DEBUGSTREAM = Devnull()
 NEWLINE = '\n'
-EMPTYSTRING = ''
 COMMASPACE = ', '
 DATA_SIZE_DEFAULT = 33554432
 
@@ -122,12 +121,28 @@
     max_command_size_limit = max(command_size_limits.values())
 
     def __init__(self, server, conn, addr, data_size_limit=DATA_SIZE_DEFAULT,
-                 map=None):
+                 map=None, decode_data=None):
         asynchat.async_chat.__init__(self, conn, map=map)
         self.smtp_server = server
         self.conn = conn
         self.addr = addr
         self.data_size_limit = data_size_limit
+        if decode_data is None:
+            warn("The decode_data default of True will change to False in 3.6;"
+                 " specify an explicit value for this keyword",
+                 DeprecationWarning, 2)
+            decode_data = True
+        self._decode_data = decode_data
+        if decode_data:
+            self._emptystring = ''
+            self._linesep = '\r\n'
+            self._dotsep = '.'
+            self._newline = NEWLINE
+        else:
+            self._emptystring = b''
+            self._linesep = b'\r\n'
+            self._dotsep = b'.'
+            self._newline = b'\n'
         self.received_lines = []
         self.smtp_state = self.COMMAND
         self.seen_greeting = ''
@@ -287,11 +302,14 @@
             return
         elif limit:
             self.num_bytes += len(data)
-        self.received_lines.append(str(data, "utf-8"))
+        if self._decode_data:
+            self.received_lines.append(str(data, 'utf-8'))
+        else:
+            self.received_lines.append(data)
 
     # Implementation of base class abstract method
     def found_terminator(self):
-        line = EMPTYSTRING.join(self.received_lines)
+        line = self._emptystring.join(self.received_lines)
         print('Data:', repr(line), file=DEBUGSTREAM)
         self.received_lines = []
         if self.smtp_state == self.COMMAND:
@@ -300,6 +318,8 @@
                 self.push('500 Error: bad syntax')
                 return
             method = None
+            if not self._decode_data:
+                line = str(line, 'utf-8')
             i = line.find(' ')
             if i < 0:
                 command = line.upper()
@@ -330,12 +350,12 @@
             # Remove extraneous carriage returns and de-transparency according
             # to RFC 5321, Section 4.5.2.
             data = []
-            for text in line.split('\r\n'):
-                if text and text[0] == '.':
+            for text in line.split(self._linesep):
+                if text and text[0] == self._dotsep:
                     data.append(text[1:])
                 else:
                     data.append(text)
-            self.received_data = NEWLINE.join(data)
+            self.received_data = self._newline.join(data)
             status = self.smtp_server.process_message(self.peer,
                                                       self.mailfrom,
                                                       self.rcpttos,
@@ -577,10 +597,17 @@
     channel_class = SMTPChannel
 
     def __init__(self, localaddr, remoteaddr,
-                 data_size_limit=DATA_SIZE_DEFAULT, map=None):
+                 data_size_limit=DATA_SIZE_DEFAULT, map=None,
+                 decode_data=None):
         self._localaddr = localaddr
         self._remoteaddr = remoteaddr
         self.data_size_limit = data_size_limit
+        if decode_data is None:
+            warn("The decode_data default of True will change to False in 3.6;"
+                 " specify an explicit value for this keyword",
+                 DeprecationWarning, 2)
+            decode_data = True
+        self._decode_data = decode_data
         asyncore.dispatcher.__init__(self, map=map)
         try:
             self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
@@ -599,7 +626,7 @@
     def handle_accepted(self, conn, addr):
         print('Incoming connection from %s' % repr(addr), file=DEBUGSTREAM)
         channel = self.channel_class(self, conn, addr, self.data_size_limit,
-                                     self._map)
+                                     self._map, self._decode_data)
 
     # API for "doing something useful with the message"
     def process_message(self, peer, mailfrom, rcpttos, data):
diff --git a/Lib/test/test_smtpd.py b/Lib/test/test_smtpd.py
index 93f14c4..db1f52b 100644
--- a/Lib/test/test_smtpd.py
+++ b/Lib/test/test_smtpd.py
@@ -7,13 +7,18 @@
 
 
 class DummyServer(smtpd.SMTPServer):
-    def __init__(self, localaddr, remoteaddr):
-        smtpd.SMTPServer.__init__(self, localaddr, remoteaddr)
+    def __init__(self, localaddr, remoteaddr, decode_data=True):
+        smtpd.SMTPServer.__init__(self, localaddr, remoteaddr,
+                                  decode_data=decode_data)
         self.messages = []
+        if decode_data:
+            self.return_status = 'return status'
+        else:
+            self.return_status = b'return status'
 
     def process_message(self, peer, mailfrom, rcpttos, data):
         self.messages.append((peer, mailfrom, rcpttos, data))
-        if data == 'return status':
+        if data == self.return_status:
             return '250 Okish'
 
 
@@ -31,9 +36,9 @@
         smtpd.socket = asyncore.socket = mock_socket
 
     def test_process_message_unimplemented(self):
-        server = smtpd.SMTPServer('a', 'b')
+        server = smtpd.SMTPServer('a', 'b', decode_data=True)
         conn, addr = server.accept()
-        channel = smtpd.SMTPChannel(server, conn, addr)
+        channel = smtpd.SMTPChannel(server, conn, addr, decode_data=True)
 
         def write_line(line):
             channel.socket.queue_recv(line)
@@ -45,6 +50,10 @@
         write_line(b'DATA')
         self.assertRaises(NotImplementedError, write_line, b'spam\r\n.\r\n')
 
+    def test_decode_data_default_warns(self):
+        with self.assertWarns(DeprecationWarning):
+            smtpd.SMTPServer('a', 'b')
+
     def tearDown(self):
         asyncore.close_all()
         asyncore.socket = smtpd.socket = socket
@@ -57,7 +66,8 @@
         self.debug = smtpd.DEBUGSTREAM = io.StringIO()
         self.server = DummyServer('a', 'b')
         conn, addr = self.server.accept()
-        self.channel = smtpd.SMTPChannel(self.server, conn, addr)
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr,
+                                         decode_data=True)
 
     def tearDown(self):
         asyncore.close_all()
@@ -502,6 +512,12 @@
         with support.check_warnings(('', DeprecationWarning)):
             self.channel._SMTPChannel__addr = 'spam'
 
+    def test_decode_data_default_warning(self):
+        server = DummyServer('a', 'b')
+        conn, addr = self.server.accept()
+        with self.assertWarns(DeprecationWarning):
+            smtpd.SMTPChannel(server, conn, addr)
+
 
 class SMTPDChannelWithDataSizeLimitTest(unittest.TestCase):
 
@@ -512,7 +528,8 @@
         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)
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr, 32,
+                                         decode_data=True)
 
     def tearDown(self):
         asyncore.close_all()
@@ -553,5 +570,92 @@
                          b'552 Error: Too much mail data\r\n')
 
 
+class SMTPDChannelWithDecodeDataFalse(unittest.TestCase):
+
+    def setUp(self):
+        smtpd.socket = asyncore.socket = mock_socket
+        self.old_debugstream = smtpd.DEBUGSTREAM
+        self.debug = smtpd.DEBUGSTREAM = io.StringIO()
+        self.server = DummyServer('a', 'b', decode_data=False)
+        conn, addr = self.server.accept()
+        # Set decode_data to False
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr,
+                decode_data=False)
+
+    def tearDown(self):
+        asyncore.close_all()
+        asyncore.socket = smtpd.socket = socket
+        smtpd.DEBUGSTREAM = self.old_debugstream
+
+    def write_line(self, line):
+        self.channel.socket.queue_recv(line)
+        self.channel.handle_read()
+
+    def test_ascii_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'plain ascii text')
+        self.write_line(b'.')
+        self.assertEqual(self.channel.received_data, b'plain ascii text')
+
+    def test_utf8_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'utf8 enriched text: \xc5\xbc\xc5\xba\xc4\x87')
+        self.write_line(b'and some plain ascii')
+        self.write_line(b'.')
+        self.assertEqual(
+            self.channel.received_data,
+            b'utf8 enriched text: \xc5\xbc\xc5\xba\xc4\x87\n'
+                b'and some plain ascii')
+
+
+class SMTPDChannelWithDecodeDataTrue(unittest.TestCase):
+
+    def setUp(self):
+        smtpd.socket = asyncore.socket = mock_socket
+        self.old_debugstream = smtpd.DEBUGSTREAM
+        self.debug = smtpd.DEBUGSTREAM = io.StringIO()
+        self.server = DummyServer('a', 'b')
+        conn, addr = self.server.accept()
+        # Set decode_data to True
+        self.channel = smtpd.SMTPChannel(self.server, conn, addr,
+                decode_data=True)
+
+    def tearDown(self):
+        asyncore.close_all()
+        asyncore.socket = smtpd.socket = socket
+        smtpd.DEBUGSTREAM = self.old_debugstream
+
+    def write_line(self, line):
+        self.channel.socket.queue_recv(line)
+        self.channel.handle_read()
+
+    def test_ascii_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'plain ascii text')
+        self.write_line(b'.')
+        self.assertEqual(self.channel.received_data, 'plain ascii text')
+
+    def test_utf8_data(self):
+        self.write_line(b'HELO example')
+        self.write_line(b'MAIL From:eggs@example')
+        self.write_line(b'RCPT To:spam@example')
+        self.write_line(b'DATA')
+        self.write_line(b'utf8 enriched text: \xc5\xbc\xc5\xba\xc4\x87')
+        self.write_line(b'and some plain ascii')
+        self.write_line(b'.')
+        self.assertEqual(
+            self.channel.received_data,
+            'utf8 enriched text: żźć\nand some plain ascii')
+
+
 if __name__ == "__main__":
     unittest.main()