I know I’m a bit late with this but for everyone who used my info to configure their mailserver needs to know this even if it is late. I don’t have a record who is using my setup and therefore I have no others means than posting this and hoping you will read this. I found out the hard way by trying to email someone who uses my setup and to find out my mails are rejected. I got emails returned with the error message:
host mail.domain.tld[xx.xx.xx.xx] said: 554 Service
unavailable; Client host [yy.yy.yy.yy] blocked using opm.blitzed.org (in
reply to RCPT TO command)

It was to do with the line
reject_rbl_client opm.blitzed.org
in the configuration of /etc/postfix/main.cf

By trying to find out why I was getting rejected, I got worried I was being tagged as a spamserver, I found out that opm.blitzed.org has shutdown it’s service. They shutdown in May 2006, I wonder why I haven’t noticed it earlier. The reasons where technical and you can read more on it here.

My advice is, if you still have the above line in your main.cf please remove it until the service is back up again. I’m very sorry if this has caused any inconvenience.