Horde not working in Plesk 8.3

I bought a virtual dedicated server in godaddy.com taht came with plesk preinstalled.
It´s a Linux server with fedora core 7.

I´ve been trying to change the ip/subnet in the mail > whitelist section of plesk to prevent from having an open relay that was causing the server to have the smtp daliy limit to be reached by someone using my server as relay.

I tried to change Plesk from default 127.0.0.1/8, which leaves you with an open relay and so i tried 127.0.0.1/32.
After thar i couldn´t access webmail anymore. Webmail can be found in webmail.mydomains.com.
When i enter the webmails of alll my domains, it appears the classical horde login screen, you can take a look at it in http://webmail.latinarte.com/ but when I try to login nothing works.

So i tried to restore the settings to 127.0.0.1/8 but plesk gives an error that says IP adress/net mask pair is invalid. Anybody knows why does it gives that error?

I wnat to know if someone can help me find the way to restore it back to it´s original way.

Can i use 127.0.0.1/32 and have the webmail working?

Thanks in adavnce.