kill open relay exch 5.5 multi domains

I need to disable open relay on Exchange 5.5, Win2k network Active Directory. We have multiple domains going through the mail server.

I tried going into IMC, Routing, set each domain’s “sent to” and “route to” its domain name, then went to routing restrictions and set to only allow hosts that have successfully authenticated. This worked fine to kill open relay, but then the clients could not send or recieve emails beyond the mail server.

Do I need to go into “Connections” in IMC and set have all hosts authenticate then instruct the clients to make changes in their email client to accommodate this?

Suggestions on how to conquer this are greatly appreciated!