Or indeed, not working at all! I had the issue of it working one way only (On-Premise Exchange organization > Office 365) but the other way (cloud to on-premise) did not work at all.
The answer is shown in this video
This covers the reasons why Free/Busy (and the other federation features of MailTips, archive and move mailbox might not work both ways in a Hybrid Coexistence setup for Office 365 or between two Exchange on-premise organizations.
The reason I found was the Organization Relationship contained the wrong list of domains. There are three domains (at least) that are needed in the organization relationship. These are:
- Primary SMTP Namespace Domain (i.e. fabrikam.com)
- Namespace for other organization (i.e. service.fabrikam.com)
- Exchange Delegation domain (i.e. exchangedelegation.fabrikam.com)
In the organization relationship on-premise (or Org A if you are doing two on-premise organizations) set the following domains after the relationship is created. This includes the primary SMTP namespace and the service namespace for the other organization. This can be set with the following Exchange Management Shell cmdlet:
Set-OrganizationRelationship -Identity "To Cloud" -DomainNames "service.fabrikam.com","fabrikam.com" -MailTipsAccessEnabled $True -MailTipsAccessLevel All -DeliveryReportEnabled $True –TargetOwaUrl https://outlook.com/owa/fabrikam.com -ArchiveAccessEnabled $True –MailboxMoveEnabled $True
In Org B (or on Office 365) use a similar cmdlet, but use the Exchange Delegation namespace and the primary SMTP domain. Also Office 365 does not let you set the MailboxMoveEnabled property to $True
Set-OrganizationRelationship -Identity "To On-premises" -DomainNames "exchangedelegation.fabrikam.com","fabrikam.com" -MailTipsAccessEnabled $True -MailTipsAccessLevel All -DeliveryReportEnabled $True -ArchiveAccessEnabled $True
Supposedly Service Pack 2 for Exchange 2010 will do all this and more for you with the Hybrid Configuration Wizard, but its always useful for troubleshooting to discover what changes and why when you run a wizard to do things!