In an Exchange 2003 and Office 365 Hybrid Deployment environment, the Office 365 users are able to view the Free/Busy information of Exchange 2003 users or resources. However, the Exchange 2003 user may not be able to view the Free/Busy information of the Office 365 users or resources unexpectedly.
Many configuration issues may cause this to occur. In the case of my customer, the cause was to change the permission for the free/busy folder from the Default Permission: Author to Editor as described here:
This can be accomplished in the Exchange 2003 System Manager. Right click on folder with the EXTERNAL name and select properties.
Click Client Permissions
Change the Default Permission from Author to Editor
If you are lucky, this will solve the problem for you. If not, there are a few other things to try.
The first issue that you should be aware of is that Outlook Web Access (OWA) cannot view free/busy for a mailbox that resides in Exchange Online.
http://community.office365.com/en-us/wikis/officeapps/558.aspx
There are some articles that recommend setting the LegacyExchangeDN parameter in mailboxes but I did not have to do that. http://technet.microsoft.com/en-us/library/hh310374.aspx
http://community.office365.com/en-us/wikis/officeapps/558.aspx
http://community.office365.com/en-us/forums/162/t/55245.aspx
There are also articles that recommend hardcoding the targetsharingepr record but I think that was only necessary when Exchange Online was in Beta. For example, they said to run this command
Set-OrganizationRelationship “CompanyABC” -TargetSharingEpr https://mail.companyabc.com/EWS/Exchange.asmx/WSSecurity
http://blogs.technet.com/b/neiljohn/archive/2011/08/15/office-365-hybrid-deployment-exchange-rich-coexistence-sharing-availability-free-busy.aspx
Again, I don’t think that is necessary with the current builds because it is not mentioned in the Exchange Deployment Assistant documentation.
There are also issues with routing group configuration that could cause problems with free/busy. One of our other customers ran into this so you should see whether this impacts you: http://blogs.technet.com/b/messaging_with_communications/archive/2011/09/09/office365-exchange-2003-free-busy-coexistence.aspx
One helpful technique to isolate the issue is to create a user on the Exchange 2010 Hybrid server. If the user can view free/busy for Exchange Online mailboxes, then the issue is isolated to public folder configuration since Exchange 2010 users do not rely on PF for free/busy. However, if a Exchange 2010 mailbox cannot view Exchange online free/busy, then the problem could be with the organizational relationship and autodiscover DNS records.
http://support.microsoft.com/kb/2555008
Another article I found helpful was to validate that the free/busy folders exist to begin with.
http://support.microsoft.com/kb/2555008
Original blog post with images is available here:
The Cloud Technologist 