[FIX] P3: cross-version smtplib/email changes

* SMTPLib[P3] uses a debug method on ``SMTP`` rather than a global
  ``stderr``
* email.Encoders is a deprecated & outdated (since 2006) alias for
  email.encoders

odoo/addons/base/ir/ir_mail_server.py

 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from email import Encoders
+from email import encoders
 from email.charset import Charset
 from email.header import Header
 from email.mime.base import MIMEBase
@@ -28,16 +28,16 @@ class MailDeliveryException(except_orm):
     def __init__(self, name, value):
         super(MailDeliveryException, self).__init__(name, value)
 
+# Python 3: patch SMTP's internal printer/debugger
+def _print_debug(self, *args):
+    _logger.debug(' '.join(str(a) for a in args))
+smtplib.SMTP._print_debug = _print_debug
 
+# Python 2: replace smtplib's stderr
 class WriteToLogger(object):
-    """debugging helper: behave as a fd and pipe to logger at the given level"""
-    def __init__(self, logger, level=logging.DEBUG):
-        self.logger = logger
-        self.level = level
-
     def write(self, s):
-        self.logger.log(self.level, s)
-
+        _logger.debug(s)
+smtplib.stderr = WriteToLogger()
 
 def try_coerce_ascii(string_utf8):
     """Attempts to decode the given utf8-encoded string
@@ -159,14 +159,6 @@ class IrMailServer(models.Model):
                                                                   "is used. Default priority is 10 (smaller number = higher priority)")
     active = fields.Boolean(default=True)
 
-    def __init__(self, *args, **kwargs):
-        # Make sure we pipe the smtplib outputs to our own DEBUG logger
-        if not isinstance(smtplib.stderr, WriteToLogger):
-            logpiper = WriteToLogger(_logger)
-            smtplib.stderr = logpiper
-            smtplib.stdout = logpiper
-        super(IrMailServer, self).__init__(*args, **kwargs)
-
     @api.multi
     def name_get(self):
         return [(server.id, "(%s)" % server.name) for server in self]
@@ -371,7 +363,7 @@ class IrMailServer(models.Model):
                 part.add_header('Content-Disposition', 'attachment', filename=filename_rfc2047)
 
                 part.set_payload(fcontent)
-                Encoders.encode_base64(part)
+                encoders.encode_base64(part)
                 msg.attach(part)
         return msg