POP account authentication on OD slave server

I have a remote site used for disaster recovery that is set up as an OD slave on a separate domain but same Kerberos realm. I need to do some testing with the POP server on that machine (Xserve running 10.4.10, same as OD master). I set up Applemail with a 2nd account pointing to that POP server. However, I cannot authenticate to that server. It says it is not recognizing the username. Should I not be able to use the same username to authenticate on all OD slaves? Is there something messed up with the config on that slave or can I just not do what I want? TIA.