estimation_id = fields.Many2many('res.users', default=lambda self:self.env.user, domain=lambda self: [("groups_id", "=",self.env.ref( "estimation.group_user_hide" ).id)], index=True, track_visibility='onchange', string='Estimation Asign To')

new_user_ids = [user.id for user in rec.estimation_id if user.id not in user_ids[rec.id]]

when i used above field that time i got selected user's user_id but i also need to get the email_id of user.