It sounds like you are using native Domino. Just to double check. When you open stconfig.nsf do you see the highlighted document? If you don't then it's using the address book populated on the Community server. In this case it should "just work."
If you have an LDAPServer document then provide the data from the document, remming out the user name and password.
You can enable trace on the client using the instructions in http://www-01.ibm.com/support/knowledgecenter/SSKTXQ_8.5.0/com.ibm.help.sametime.v85.doc/trouble/trbl_client_log_trace.html
and find the location of the workspace directory from http://www-01.ibm.com/support/knowledgecenter/SSKTXQ_8.5.0/com.ibm.help.sametime.v85.doc/trouble/trbl_client_locate_wsp.html?lang=en