If you have a two-way forest trust in place between two organizations, such as during a merger, you can share calendar free/busy information between two Exchange organizations without having to configure federated delegation.
|Federated delegation between contoso.com and fabrikam.com|
- Run the following cmdlet in the target domain:
Get-ClientAccessServer | Add-AdPermission -AccessRights ExtendedRight -ExtendedRights “ms-exch-epi-token-serialization” -User “sourcedomain\Exchange Servers”
- Run the following two cmdlets in the source domain:
Add-AvailabilityAddressSpace -ForestName targetdomain.com -AccessMethod PerUserFB -UseServiceAccount $true
Export-AutodiscoverConfig -TargetForestDomainController dc.remotedomain.com -TargetForestCredential $Target -MultipleExchangeDeployments $true
After these steps are performed the users in the source domain can see free/busy information for users in the target domain. Repeat these steps, switching the the source and target domains, to allow bidirectional free/busy look-ups.
Be aware that the source domain relies on Autodiscover and Exchange Web Services (EWS) in the target domain. If Autodiscover is not configured properly (i.e., missing the autodiscover.targetdomain.com record in DNS) it will not work. It also relies on the externalUrl property of the WebServicesVirtualDirectory in the target domain. That must be set to a valid URL and the SSL certificate used by this EWS URL must be trusted by the source domain.