AADSTS53003 – Access Blocked by Conditional Access Policy
Error: AADSTS53003 – Access has been blocked by Conditional Access policies. The policy does not allow token issuance.
This error occurs when a Conditional Access policy in the customer tenant blocks access to the Sync 365 service principal or delegated admin account.
Cause: The customer tenant has a policy that restricts access from external users or apps — including those used by Sync 365 — and hasn’t excluded the appropriate accounts or service principals.
How to Identify the Policy
- Login to the customer's Azure portal
- Open Microsoft Entra ID (Azure AD)
- Go to Users → Sign-in logs
- Select User sign-ins (non-interactive)
- Filter by application name "Sync 365 License"
- Click into the failed sign-in
- Click Conditional Access policy to see any applied.
- Look for one with a Blocked Result to find the one that is blocking it.
Resolution
To fix the issue, adjust the Conditional Access policies in the customer tenant:
- Login to the customer’s Microsoft Entra ID portal
- Go to Conditional Access → Policies
- Identify the policy blocking access in the Sign-in logs
- Edit the policy and make the following changes:
- In the Users section, click Exclude → select "Service provider users"
- All: excludes all service providers with tenant relationships
- Select: allows you to specify specific tenant IDs — be sure to enter your tenant ID
- Save the policy and retry the connection in Sync 365
More guidance:
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