We have a domain that has a distribution list which contains external contacts - this works as desired. The customer would like to add these external contacts to the GAL. For instance, customer is @abc.com and external contacts are @xyz.com - I can't see how this is possible without adding the domain of xyz.com which would then take up licenses and obviously cause other potential problems.
Am I missing something here? I know in Exchange you can add Mail Contacts and they can appear in the GAL.