Target OU is in a child domain in the target forest. You may want to set the Target Search Base DN to the root of the forest on the target location information section of the Notes to Exchange connector.
For example: Exchange domain is in the forest root domain: domain.com. There is a child domain: child.domain.com and the connector is targeting an OU in child.domain.com
During the configuration, only child.domain.com is available for selecting as the Target Search Base DN. You are not able to select domain.com to search both parent (domain.com) and child domain (child.domain.com). Active Directory account is used within this connector can search the entire forest. These domains are also trusted.
STATUS
Enhancement request TFS329528 has been submitted to Development for consideration in a future release of Coexistence Manager for Notes.