Hi, I'm hoping to get confirmation on the following (2) AD/Exchange designs. I've finding nothing but conflicting information about these designs online.Design A:There are (2) AD forests withan Exchange 2007 server in Forest A. Each Forest has a single Domain. Would it be possible to setup a trust between Forest A and Forest B so that user accounts in the domain of Forest B can have mailboxes in the Exchange server in the domain of Forest A with single sign-on? Also, if this is possible, would there be any issues with "Free/Busy - Availability" between users in Forest A and Forest B? Lastly, would there any issues with replicating GALs or is there a need for a 3rd party.Design B:There are (2) AD forest with an Exchange 2007 server in BOTH Forests. We'd like to be able to integrate the Exchange environment so that we can have a replicated GAL and be able to see "Free/Busy - Availability" of users between both Exchange servers. I'm not sure if this is even possible. Please someone confirm. Thanks in advance for your help on this.

Hi,1. Do you say one forest for just user accounts and another forest is dedicated for Exchange server then it looks like Resource Forest scenario otherwise it is similar to your second question and answer is cross forest. Refer below article to find out the type of topology you want.Active Directory Forest Topologies http://technet.microsoft.com/en-us/library/bb124765.aspx Some of the reference for Resource Forest Topology.How to Deploy Exchange 2007 in an Exchange Resource Forest Topology http://technet.microsoft.com/en-us/library/aa998031.aspxhttp://www.msexchange.org/articles_tutorials/exchange-server-2007/planning-architecture/deploying-exchange-resource-forest-part1.htmlhttp://www.msexchange.org/articles_tutorials/exchange-server-2007/planning-architecture/deploying-exchange-resource-forest-part2.html 2. In cross forest if you want to sync the GAL of two different forests then you need to do it with ILM 2007 Feature Pack 1. How to Deploy Exchange 2007 in a Cross-Forest Topologyhttp://technet.microsoft.com/en-us/library/aa998597.aspx Here is the procedure to configure Free/Busy availability service in cross-forest. How to Configure the Availability Service for Cross-Forest Topologies http://technet.microsoft.com/en-us/library/bb125182.aspxAmit Tank || MVP - Exchange || MCITP - Exchange 2007 || http://ExchangeShare.WordPress.com

Hi Amit, Thanks for the info. I'm going to spend some time reading over the articles tonight.

Actually, what I'm looking to do is more like a mixture of a cross-forest topology and a resource forest topology. In other words, one exchange server in one forest with usersand another forest with another set of users without an exchange server but leveraging the same exchange server in the other forest via a trust. I have a picture of this topology which I can share if it would help in illustrating the intended design. Please let me know if this makes sense and if it is possible. Thanks.

Hello, In that case you need to create linked mailboxes for the users of another trusted forest.How to Create a Linked Mailboxhttp://technet.microsoft.com/en-us/library/bb123524.aspx Amit Tank || MVP - Exchange || MCITP - Exchange 2007 || http://ExchangeShare.WordPress.com

Hi I understand that you want to deploy single Exchange Organization with 2 forests. Then I recommend you to deploy one Exchange forest with two Account forests. I think that could be the better deployment. Please refer to the real deployment guide from article below: Deploying an Exchange Resource Forest (Part 1) Deploying an Exchange Resource Forest (Part 2) Best regards, Xiu