Note: In order for Free/Busy to work Outlook Anywhere needs to be enabled in both forest and auto discover needs to be functioning properly. Additionally, the external URLs for EWS need to be configured.
Note: A service account in each forest is required for authentication purposes. This account should not have a mailbox and the minimum amounts of rights possible. In the example configuration it has been configured as “\svc_fb”.
Step 1: Open the Exchange management shell
Note: Step 2 relates to the target forest. This is the forest you are pulling the information to.
Step 2: Run “Set-AvailabilityConfig -OrgWideAccount ‘\svc_fb’”
Step 3: Run “$a = Get-Credential (Enter the credentials for organization-wide user the domain you want to get Free/Busy from)”
Step 4: Run “Add-AvailabilityAddressspace -Forestname Contoso.com -Accessmethod OrgWideFB -Credential:$a”
 | Coexistence between Exchange forests (without trusts…) -- Part 9: Synchronization! |
 | Coexistence between Exchange forests (without trusts…) -- Part 11: References |