@Jayko, Jason , From your description, I know you want to block outlook access mailbox on non company device. If there's any misunderstanding, please let us know.
If this is related to Office 365 or exchange online access, we can configure a conditional access policy to only allow compliant device to access. The main configuration can be as below:
- Enroll these devices into Intune. Configure Intune compliance policy to make all the company device as compliant.
https://learn.microsoft.com/en-us/mem/intune/protect/device-compliance-get-started - Create conditional access policy with the following main setting:
-Users and groups: chosee the user group we want to apply this policy.
- Cloud apps or action: Choose Office 365 or exchange online.
- Conditions: choose the device platform and client app (For outlook, we can select mobile apps and desktop clients. For browser access, we can choose Browser)
- Access control-Grant access and select "Require device to be marked as compliant"
-Enable policy:ON.
We can see more details in the following link:
https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/overview
https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/plan-conditional-access
Hope it can help.
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