Exchange problem

I have a site where they are using Exchange 5.5, Outlook 2000 as the client but they were set up as using Pop3 as there email protocol. We were alerted by their ISP that their site was being used by a spammer for relaying emails. I changed the IMSsetting on the Exchange server to the setting per Technet directions

Checked the reroute incoming SMTP mail- and
checked the Hosts and clients with these IP address -on the routing restrictions tab, but left the list blank.
Now they are unable to sent any email, they can receive. Can anyone please help!
Thanks