I recently ran into a situation where some Linux based Thunderbird users needed access to the Exchange 2010 GAL.  Here were the settings that work.\nThe most important thing you should be aware of is you are not accessing Exchange technically.  You need to point your clients at your global catalog server.  Which is going to be hosted on one of your domain controllers.\nName: Not Important\nHostname: GlobalCatalog-01.domain.local\nBase DN: dc=domain,dc=local\nPort number: 3268\nBind DN:  CN=Username,OU=Users,DC=Domain,DC=local  <-- This of course should be the location of your user account in active directory\nBind DN:  domainusername  <--This is a simpler approach