'The \'default\' attribute of the \'prefs\' element MUST be one of the following values:
\'always\' - all messages are archived by default.
\'never\' - messages are never archived by default.
\'roster\' - messages are archived only if the contact\'s bare JID is in the user\'s roster.'

def set_preferences(self, default=None, always=None, never=None, block=True, timeout=None, callback=None):

    iq = self.xmpp.Iq()
    iq['type'] = 'set'
    iq['mam_prefs']['default'] = default
    iq['mam_prefs']['always'] = always
    iq['mam_prefs']['never'] = never
    return iq.send(block=block, timeout=timeout, callback=callback)
