Binding Member Server: Add a server to be strictly a Mail server

I am working through a course that requires me to work through some command-line. No problem. However, I have been stuck on how the questions is phrased and how to accomplish it. The task is binding to member servers. (Like adding a server to be used stricly for mail). I am to do so using the CLI only. Does this translate to setting an Open Directory server to bind to an Open Directory master using Mail services? If so, how would that be accomplished via CLI. If I am intererupting this incorrectly then please let me know. I would appreciate any feedback.

Thanks