Currently, if Outline mode is turned on, Material ID is not available. It would be helpful if this is corrected and there is no longer a need to render the same image two times in order to have all channels needed for post processing. It would also work if the Outline was a separate channel on it’s own. Something like the AO options work now… there is an option to render out a separate AO channel and an option to show AO in the viewport and rendered with the Beauty pass.