PEAR has had PHP support for SURBLs and other blacklists since January
2005 via the Net_DNSBL package:
http://pear.php.net/manual/en/package.networking.net-dnsbl.php
but a very early version of Net_DNSBL did not properly cache DNS
queries. If you are using PEAR's Net_DNSBL, please make sure you're
using a recent version.
Given that PEAR is a widely used PHP component framework, it's
possible Net_DNSBL queries are built into many different applications.
Any recent applications should be fine, but it may be worth checking
any old versions for updates or to generally update your PEAR
versions.
We'd like to welcome the addition of a new SURBL public name
server d5.surbl.org hosted by:
Kuehlbox Networks
The SURBL community thanks all the hosts and administrators of
the public name servers for their ongoing help and support!