We have 150 users moved to Exchange 2013 as are pilot.   These users including my account have difficulty scheduling meetings.  When reviewing free/busy data, users who are still on Exchange 2010 display and hash marks for availability.  Pressing Alt-k  will refresh and eventually display free/busy, but takes several minutes, and some users may never display free/busy info.

Any ideas on how to resolve?  Other than quickly moving the remaining 3500 users to 2013.

Thanks

Look in the event logs of the Exchange 2013 server for warnings or errors with the Availability Service.  The Exchange 2013 server is having trouble connecting to the Availability Service on the Exchange 2010 server.  That's served up by the Exchange Web Services (EWS) virtual directory.  Make sure that's properly configured.

Hi Tony,

Thank you for your question.

In addition Eds suggestion.

Did the issue occur on OWA and outlook?

Are there any other issue which is about connectivity between Exchange 2013 and Exchange 2010?

If there are any errors in application log, we could refer to the following link to rebuild EWS virtual directory to check if the issue persist:

https://technet.microsoft.com/en-us/library/ff629372%28v=exchg.141%29.aspx

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim

Discovered the issue:  2013 Mailbox servers will query all CAS servers, including external facing for 2010 account Free/Busy.

When querying the external facing CAS, external addresses that were outside of the firewall would timeout, causing very slow performance as it would try again on next server until success.

domain.local - no issues

domain.com - fail on traversing firewall.

Added to local hosts file on 2013 mailbox servers with internal IP Address of external CAS names:

      192.168.x.x mail.domain.com

We do not have split-brain DNS setup, this is another reason for setting up split-brain DNS.

Ed, thanks for narrowing down to the "Availability Service".

The specific event in the application log that catches the issue is "MSExchange Availability" Event ID: 4002.  This event is only found on the servers hosting the 2013 mailbox role.  2013 Mailbox servers perform all proxies to other mailboxes including to legacy Exchange.