We have another business unit that's on our WAN but with it's own AD, domain, Exchange server (2007). They have AD accounts on our domain and they're password syncronized, but don't have mailboxes on our Exchange server. I need a way to allow them to access the calendar for a room resource that we use as a shared calender in our group. Since Outlook can't connect two two Exchange servers, I can't even just give them permssions. We have SharePoint and used to use that for the shared calendar, but it's not (yet) Exchange enabled, so meeting requests had to be scheduled in Outlook/Exchange, then recreated on the SharePoint calender, and people revolted. It may be months before IT can get the Exchange/SharePoint item in a sprint, so sharing the Exchange based calendar is my only real resource. Thanks, --Stan

hi, you can start by looking at this post by nick http://knicksmith.blogspot.com/2007/05/managing-resource-mailbox-calendars.html and this thread too http://social.technet.microsoft.com/Forums/en-US/exchangesvradmin/thread/48382744-0011-4331-a548-732d65b3308b

Please see the similar post as Damilola mentioned, a related article for you reference: How to Configure the Availability Service for Cross-Forest Topologies http://technet.microsoft.com/en-us/library/bb125182(EXCHG.80).aspx Thanks, Elvis