I came across an issue with a clients Exchange Server deployment today that is not well documented – or rather it is, but you need to know where to look. So I thought I would document the troubleshooting steps and the fix here.
We specifically came across this error when testing Free/Busy for an Office 365 migration, though it could happen for a variety of reasons. Free/Busy and other lookups in a cross-forest Exchange Server deployment require a working organization configuration and this was failing. Running Test-FederationTrust (a prerequisite of the organization relationship) in verbose mode (add -Verbose to the end) returned the following:
Unable to retrieve federation metadata from the security token
service. Reason: Microsoft.Exchange.Management.FederationProvisioning.FederationMetadataException: Unable to access the
Federation Metadata document from the federation partner. Detailed information: “The underlying connection was closed:
Could not establish trust relationship for the SSL/TLS secure channel.”.
The final result of the test will also show two errors for “Unable to retrieve federation metadata from the security token service.” and “Failed to request delegation token.”
The last part of the verbose error is the clue here. The server in question is unable to make an SSL/TLS connection to the endpoint that the federation trust needs to reach to get the federation trust metadata. That endpoint is listed right at the start of the Verbose output. It reads:
VERBOSE: [16:53:08.306 GMT] Test-FederationTrust : Requesting Federation Metadata from
https://nexus.microsoftonline-p.com/FederationMetadata/2006-12/FederationMetadata.xml.
Now that we have a URL and an error message, check that the URL is reachable from each of your Exchange Servers. At my client today we found one server could not successfully reach this endpoint without an SSL error turning up in the browser. The problem was that the certificate that the endpoint is secure with is issued by the Baltimore Cybertrust Root Certificate – one that Microsoft uses for lots of services, but the root certificate was not installed on that machine. Lots of root certs where missing from that machine as it had never had a root certificate update applied to it.
We installed the latest Root Certificate Update and then the federation trust worked and free/busy etc. (mail tips, cross-forest message tracking etc.) all worked fine.
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