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Fix ActiveSync Certificate Authentication HTTP 500 Errors on iPhone
Question details
Users experience repeated HTTP 500 errors when attempting to authenticate Exchange ActiveSync using certificates on iOS devices.
- Product
- Exchange ActiveSync / Microsoft Intune
- Device & OS
- iOS / iPhone
- Scenario
- Connecting an iPhone to Exchange ActiveSync using certificate-based authentication in a managed environment.
- Observed behavior
- The connection fails and returns HTTP 500 errors because the iOS device does not trust the required certificate authority chain.
Ensure you have administrator access to the Microsoft Endpoint Manager (Intune) admin center and possess the valid intermediate certificate authority .cer file required by your Exchange environment.
Deploy an iOS Trusted Root Certificate Policy via Microsoft Intune
Push the missing intermediate certificate authority to managed iPhones to establish a trusted chain and clear the authentication error.
When an iPhone lacks the intermediate certificate in its trusted root store, certificate-based authentication for ActiveSync cannot be validated, resulting in an HTTP 500 error. Deploying the certificate via Intune ensures all managed devices properly trust the connection.
Log into the Microsoft Endpoint Manager admin center, navigate to Devices > Configuration profiles, and click on 'Create profile'.
Choose 'iOS/iPadOS' as the target platform and select 'Trusted certificate' as the profile type, then click 'Create'.
Provide a name for the profile, then upload the intermediate certificate authority .cer file that is required by your Exchange server.
Assign this new trusted certificate configuration policy to the appropriate user or device groups in your organization and save the deployment.
On the affected iPhone, open the Intune Company Portal app, manually refresh to sync the latest policies, and test the ActiveSync connection again.
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Frequently Asked Questions
Why does Exchange ActiveSync return an HTTP 500 error on iOS?
This error typically occurs during certificate-based authentication when the iOS device cannot verify the Exchange server's certificate. This happens if the device is missing the intermediate or root certificates required to establish a complete chain of trust.
How can I manually check if my iPhone has the required certificates installed?
You can verify installed certificates by navigating to Settings > General > VPN & Device Management on your iPhone. Tap on the installed configuration profiles to view the specific certificates currently trusted by the device.
Can I install the required certificate without using Microsoft Intune?
Yes. While Intune is recommended for managing corporate devices in bulk, users can manually install a .cer file by downloading it via Safari, installing the downloaded profile from the Settings app, and enabling full trust for the root certificate under Settings > General > About > Certificate Trust Settings.
