Hi,
i would suggest you doing it with Conditional Access Policies in your Azure Active Directory. Here are some examples regarding Conditional Access and Mobiles https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/outlook-for-ios-and-android/secure-outlook-for-ios-and-android#blocking-outlook-for-ios-and-android
Here you can find a bit more about app protection policies https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/howto-policy-approved-app-or-app-protection#exchange-online-policy
Just as an addition, conditional access requires Azure AD Premium P1.