While I do not think that anybody is going to say that ALL RBL lists for email are a bad thing there are some problems with using them that if you are not careful can cause end users problems. In general they will help a lot but depending on how your mailserver is configured they have the potential to cause just as many heart aches.

The other day we had a few clients complaining that when they sent emails it would take 5-10 seconds most times before they were able to send from their local computer. While not a lot of time it is enough that people were complaining about it. What ended up being the problem was that an RBL list the server was using was having trouble so every time somebody sent an email the RBLs were queried and the 10 seconds was the amount of time it took for the RBL to timeout.

This particular server was Plesk so the /etc/rc.d/init.d/smtp_psa and smtps_psa is where the actual RBLs are stored. The server_args line (shown below) contains all of the lists currently being used to scan email:


server_args = /usr/sbin/rblsmtpd -r opm.blitzed.org -r rbl-plus.mail-abuse.org -r
bl.spamcop.net -r relays.ordb.org -r KR.rbl.cluecentral.net -r BR.rbl.cluecentral.net -r
blackholes.mail-abuse.org -r cbl.abuseat.org -r xbl.spamhaus.org -r sbl.spamhaus.org
/var/qmail/bin/relaylock /var/qmail/bin/qmail-smtpd /var/qmail/bin/smtp_auth
/var/qmail/bin/true /var/qmail/bin/cmd5checkpw /var/qmail/bin/true




To quickly speed up email simply remove all of the -r host.name.org to eliminate all checking and restart xinetd. While a quick fix most situations won't allow for this and the best option is to remove one at a time until it starts to work normally. In the case of the other day it turned out that ordb was the cause and once removed email functioned perfectly fine.

A little bit of googling showed that the ordb.org RBL project was shut down last month, apparently the lists were working until a few days ago when this problem started.