def multipart_content_type(boundary, subtype='mixed'):
    """Creates a MIME multipart header with the given configuration.

    Returns a dict containing a MIME multipart header with the given
    boundary.

    .. code-block:: python

        >>> multipart_content_type('8K5rNKlLQVyreRNncxOTeg')
        {'Content-Type': 'multipart/mixed; boundary="8K5rNKlLQVyreRNncxOTeg"'}

        >>> multipart_content_type('8K5rNKlLQVyreRNncxOTeg', 'alt')
        {'Content-Type': 'multipart/alt; boundary="8K5rNKlLQVyreRNncxOTeg"'}

    Parameters
    ----------
    boundry : str
        The content delimiter to put into the header
    subtype : str
        The subtype in :mimetype:`multipart/*`-domain to put into the header
    """
    ctype = 'multipart/%s; boundary="%s"' % (
        subtype,
        boundary
    )
    return {'Content-Type': ctype}