We were just acquired by a company that has its own 2007 exchange environment, @Bigcompany. We have our own exchange 2007 environment that they want to connect to, @littlecompany. How do we go about setting up some sort of secure (very secure) trust between the 2 companies so that @BigCompany can see our address book and calendars, and vice versa while we still keep our @bigcompany and @littlecompany domain names?

Hi Fannonland, Per my understanding you would like to achieve the aim of sharing the GAL and Calendar between the two domains. Actually, we need to first make the two domains trust each other. Then use the Identity Lifecycle Manager (ILM) 2007 to synchronize the GAL and Calendar. For more information, please view the resource as below: http://technet.microsoft.com/en-us/library/aa998597.aspx Hope it helps. Best Regards!

so I will need to purchase extra software to make this happen? I think the ILM 2007 is now Forefront 2010, correct? And the link in your post talks about 2010. Do we need to upgrade first? Is there no other way to connect our 2 companies besides purchasing software

You need to syncronize GAL somehow. MSFT solution for this is Forefront Identity Manager (FIM), prev. known as ILM and MIIS. BTW MIIS FP1 is free and can do this. then you need to setup autodiscover and availability services cross org. http://technet.microsoft.com/en-us/library/aa996849(EXCHG.80).aspx http://blogs.technet.com/b/exchange/archive/2011/03/04/3412075.aspx It exists other software that can syncronize GAL between Exchange org's. SimpleSync seem to work well. if you can write good script and haev good knowledge about LDAP and Exchange, you can create some script for syncing GAL. lasse at humandata dot se, http://anewmessagehasarrived.blogspot.com