Hi,

You can override the create method or write method and change the state to the required state.

please refer this

    
    @api.model
    def create(self,vals):
        vals['state'] = 'sent'
        return super(ClassName, self).create(vals)

    
    @api.multi
    def write(self,vals):
        vals['state'] = 'sent'
        return super(ClassName, self).write(vals)

Thanks