You have successfully deployed a Hybrid Configuration between your on-premises Exchange 2010 SP3 Organization and Exchange Online. Everything works as it should, except for Free/busy look-ups made from Exchange Online mailboxes to a mailbox that still resides on-premise.
You have verified that the following is OK:
- You have run ExRCA diagnostics using https://www.testexchangeconnectivity.com/ , selected the Office 365 tab and then Free/busy tests. You simulate Free/busy lookup from Online to On-premise and it works with all green lights.
- You have also followed all the troubleshooting steps presented in this Microsoft Knowledge Base article: http://support.microsoft.com/kb/2555008 – all with successfull results.
Still, when attempting to do Free/busy lookups from Online to On-premise, you get the message in Outlook or OWA saying “No information” with the reason “The external recipient’s server could not be determined”.
Settings made during your Hybrid Configuration and/or extended troubleshooting of this error have not been fully commited to Internet Information Server (IIS). Allthough the diagnostics (ExRCA etc) say that your configuration is right, vital configuration is not yet effective.
First step in resolving Free/busy errors is to follow the two steps mentioned in the Introduction to this post (ExRCA diagnostics and following KB2555008 – see above). If that does not work:
Doing iisreset on your CAS server publishing EWS/Hybrid could fix this issue.
Plan for a very short outage in Exchange services (OWA/EWS etc) and open the command prompt on your Hybrid CAS server. Then run the command iisreset
After doing IISReset, Free/busy lookups from Online to On-prem should start working within minutes.
I have seen this in the field where we spent days troubleshooting this issue on Exchange 2010SP3 hybrid configurations after finally solving it with this basic, but classic, method – restarting the services. There could of course be other reasons behind the error (i.e related to how Autodiscover is published to the internet), iisreset should not be considered as a “general cure”, but a necessary troubleshooting step if your configuration is done by the book and it still does not work.