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.
The 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.
Name: Not Important
Base DN: dc=domain,dc=local
Port number: 3268
Bind DN: CN=Username,OU=Users,DC=Domain,DC=local <– This of course should be the location of your user account in active directory
Bind DN: domainusername <–This is a simpler approach