Users in an Exchange Server 2013 environment cannot obtain free/busy information in a cross-forest setup when the number of AvailabilityAddressSpace objects exceeds 100. In this situation, the following error is returned:
Failed to get freebusy response for user:EmailAddress = <>SMTP:user@domain.com, Attendee Type = Required, Exclude Conflicts = False. Message: Unable to send cross-forest request for mailbox <UserName>SMTP:user@domain.com because of invalid configuration., inner exception: Microsoft.Exchange.InfoWorker.Common.Availability.AddressSpaceNotFoundException: Configuration information for forest/domain domain.com could not be found in Active Directory.
at Microsoft.Exchange.InfoWorker.Common.Availability.TargetForestConfigurationCache.FindByDomain(OrganizationId organizationId, String domainName)
at Microsoft.Exchange.InfoWorker.Common.Availability.QueryGenerator.GetTargetForestConfiguration(EmailAddress emailAddress)
at Microsoft.Exchange.InfoWorker.Common.Availability.TargetForestConfigurationCache.FindByDomain(OrganizationId organizationId, String domainName)
at Microsoft.Exchange.InfoWorker.Common.Availability.QueryGenerator.GetTargetForestConfiguration(EmailAddress emailAddress)