Hi Vinod,

There is a method for making any message as a to-do ( starred) in "mail.message" object. it is used in many places in Odoo.

    set_message_starred(self, cr, uid, msg_ids, starred, create_missing=True, context=None):
        """ Set messages as (un)starred. Technically, the notifications related
            to uid are set to (un)starred.
            :param bool starred: set notification as (un)starred
            :param bool create_missing: create notifications for missing entries
                (i.e. when acting on displayed messages not notified)
        """

Regards,

Hardik