'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
From_ lines in the body of the message by putting a `>\' in front of
them.
Optional maxheaderlen specifies the longest length for a non-continued
header.  When a header line is longer (in characters, with tabs
expanded to 8 spaces) than maxheaderlen, the header will split as
defined in the Header class.  Set maxheaderlen to zero to disable
header wrapping.  The default is 78, as recommended (but not required)
by RFC 2822.'

def __init__(self, outfp, mangle_from_=True, maxheaderlen=78):

    self._fp = outfp
    self._mangle_from_ = mangle_from_
    self._maxheaderlen = maxheaderlen
