SceneCaptureCube and it's Anti aliasing

I have added a SceneCaptureCube to the scene,and set it’s Anti aliasing is active.But it still hava aliasing,why?

Check to make sure you have your Scalability Settings set high enough:

On the toolbar click the “Project and Editor Settings” toolbar button, Highlight “Engine Scalability Settings”, and ensure your settings are on High or Epic. Lower settings will reduce the quality of AA (among other things).

Thank you very much for your help!I’ve set it up like you said,like this:
And I also add a PostProcessVolume like this:
But it still hava aliasing,Special attention:I said is the Export images have aliasing,not in editor.In editor it is perfect.
I mean,Why the Post Process Effects(Anti aliasing ) not working in the export images?