@Sushanth Reddy, Thanks for posting in Q&A. Based as I know, conditional access policy will apply to organization user we configured. It will not apply to the sign in request for personal account.
https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/overview
For your situation, conditional access policy can't accomplish. To Allow only work or school accounts to access outlook you can try app configuration policy in the following link:
But the above policy is only applied to managed device. So you need to enroll these devices into Intune to manage.
Hope the above information can help.
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