@MSAzure101 Thanks for posting in our Q&A.
For this issue, I didn't find there is any newer links showing difference between Outlook App and native mail client apps with regard to MDM.
Based on my research, I find that if users try to use a native e-mail app, they'll be redirected to the app store to then install the Outlook app in conditional access in our official article.
https://learn.microsoft.com/en-us/mem/intune/protect/app-based-conditional-access-intune
And intune lists the protected apps in the following article.
https://learn.microsoft.com/en-us/mem/intune/apps/apps-supported-intune-apps
So, based on my understanding, it is better to use Outlook app.
If you want to get more information, it is suggested to open an online support ticket to get more effective help. It is free. Here is the online support link.
https://learn.microsoft.com/en-us/mem/intune/fundamentals/get-support
Hope the above information will help.
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