@Rookie{} , From your description, it seems the company portal is asked to download when user access outlook on Android device. and you want to avoid the company portal download. If there's any misunderstanding, feel free to let us know.
Based as I know, the company portal app is required when we set app protection policy without enrollment for Android.
https://learn.microsoft.com/en-us/mem/intune/apps/app-protection-policy#company-portal-app-and-intune-app-protection
Meanwhile, conditional access policy with "Require device to be marked as compliant" configured can also prompt for the company portal installation.
https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/concept-conditional-access-grant
Please check if we have any app protection policy for Android or conditional access policy assigned to this user. If yes, try to exclude the policy for the user to avoid the installation of company portal.
Hope it can help.
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