diff -r 9d9c2b4850fc Doc/library/email.generator.rst
--- a/Doc/library/email.generator.rst	Fri Dec 27 14:06:15 2013 -0500
+++ b/Doc/library/email.generator.rst	Wed Jan 01 20:53:36 2014 +0400
@@ -44,7 +44,7 @@
    portable way to avoid having such lines be mistaken for a Unix mailbox format
    envelope header separator (see `WHY THE CONTENT-LENGTH FORMAT IS BAD
    <http://www.jwz.org/doc/content-length.html>`_ for details).  *mangle_from_*
-   defaults to ``True``, but you might want to set this to ``False`` if you are not
+   defaults to ``False``, but you might want to set this to ``True`` if you are
    writing Unix mailbox format files.
 
    Optional *maxheaderlen* specifies the longest length for a non-continued header.
diff -r 9d9c2b4850fc Lib/email/generator.py
--- a/Lib/email/generator.py	Fri Dec 27 14:06:15 2013 -0500
+++ b/Lib/email/generator.py	Wed Jan 01 20:53:36 2014 +0400
@@ -35,14 +35,14 @@
     # Public interface
     #
 
-    def __init__(self, outfp, mangle_from_=True, maxheaderlen=None, *,
+    def __init__(self, outfp, mangle_from_=False, maxheaderlen=None, *,
                  policy=None):
         """Create the generator for message flattening.
 
         outfp is the output file-like object for writing the message to.  It
         must have a write() method.
 
-        Optional mangle_from_ is a flag that, when True (the default), escapes
+        Optional mangle_from_ is a flag that, when True, escapes
         From_ lines in the body of the message by putting a `>' in front of
         them.
 
@@ -437,7 +437,7 @@
     Like the Generator base class, except that non-text parts are substituted
     with a format string representing the part.
     """
-    def __init__(self, outfp, mangle_from_=True, maxheaderlen=78, fmt=None):
+    def __init__(self, outfp, mangle_from_=False, maxheaderlen=78, fmt=None):
         """Like Generator.__init__() except that an additional optional
         argument is allowed.