Slow on localhost

[baba]

Hi to all.
I have installed last stable release on a linux machine in the same LAN of the mail server: it works perfectly and fast.
If i install the same release (and same configuration) on the same machine where i have the mail server, roundcube works very very slow... any suggestions?
The first machine is a Fedora 10 on vmware
The machine with the mail server is a RHEL5 on a HP ProLiant DL120.

Thanks