Hi Everyone First a quick overview over the two domains I will be taking about: Domain a) Exchange 2010 sp2 standard cals Ent server licenses mix outlook environment ~3k users Domain b) Exchange 2007 sp1 ent server and cals outlook 2010 ~1.5-2k users sharepoint for all their users The two domains have full trust between them. Okay, what we need is the following: Both A and B will need to share GAL. Both A and B will need to be able to book meeting rooms Both A and B wants to be able to open each others mailboxes (a very limited amount of people) Booking of each others meeting rooms What will happen with the licenses? What i've figured out: Booking of meeting rooms can be done once a Federation trust is up (together with sharing of contacts) Sharing of GAL is not needed if we upgrade to outlook 2010 in both domains, is that correct? "Office Outlook 2007 users can't specify SMTP addresses of external recipients to display availability information. Recipients must be picked from the GAL, which requires GAL synchronization with the external organization. Outlook 2007 users with mailboxes on Exchange 2007 Service Pack 2 (SP2) Mailbox servers can use Office Outlook Web Access on an Exchange 2007 SP2 Client Access server" Site B will need a 2010 sp2 CAS server to work as a proxy. But, what will happen with the licensing demands? Will site A need ent licenses? Can we share mailboxes between the two sites? I'm sorry for a lot of questions, but none of us have experience with federation and technet only get you so far:) Thanks in advance!

Hi, Yes, Outlook 2010 and Office Outlook Web App users can simply enter the SMTP address of an external recipient when scheduling meetings when we have federation setup between these two Organization. For CAS license, I think you can use Standard or enterprise, since Enterprise Edition CALs can be used for Exchange Standard Edition. For mailbox sharing, I think that is impossible. We can only share calendar and contact information. Xiu Zhang TechNet Community Support

Thank you for the answer. I've been looking at different kind of setups for the GAL sync, but I think FIM is a bit overkill, is there other good solutions, for just creating GAL's in both domains?

Hi, I'd like to share the article below: Deep dive into rich coexistence between Exchange Forests (Part 4) http://www.msexchange.org/articles_tutorials/exchange-server-2010/migration-deployment/deep-dive-into-rich-coexistence-between-exchange-forests-part4.html Xiu Zhang TechNet Community Support