@Redistro, Thanks for posting in Q&A. Based on my check, I only find a setting "Disable AutoDiscover (User)" in Setting Catalog policy for outlook 2016. If your outlook is 2016, you can try this setting.
However, if your outlook is with other version, there's no built-in policy to do this in Intune yet. But after researching, I find the registry key can control by registry key. You can test on one device to see if it can work.
Hope it can help.
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