I've installed my server by following the guide found in this site for FC5 and installed ISPConfig. As far as I know, everything works fine. I host multiple sites/domains on this server and some of the sites have email forms for visitors to send queries to the site owners. Somehow, this have caused me some problems with CBL, which have added my server's IP to their blacklist. According to CBL, the possible reason that my server's IP is being blacklisted could be because whenever an outgoing SMTP connection is made, the SMTP is identifying itself using the sending domain or in this case, the domain that the email form is used. CBL advised me to configure my mailserver to only use FQDN when sending mails out. I am not very familiar with Postfix, so I do not know how to set Postfix to use the FQDN name, which is the server name. Any help is greatly appreciated.