Object Class types - can they be custom?

[vtrick]

I've been trying to import a directory that someone else exporting using Exchange 5.5's directory export tool. The text file contains the header "Obj-Class," but instead of listing "Mailbox," "DL," etc., it lists "organizationalPerson|Person|Top." Exchange says this is not a recognized Obj-class type, and the import fails. Does anyone know what this is? (Is this a custom-defined Obj-Class that I have to define in my server before I can import the directory?)

Thanks!