Passive Spam Block List
The Passive Spam Block List, or PSBL, uses the
which works in a really simple way.
If one of my spamtraps receives email from a certain IP address, then
that IP address gets listed. After a certain time the IP address
times out and is automatically dropped from the list. However, if
the IP address contains a real mail server, most likely one of the
users of the mail server is going to notice the listing and will
remove the mail server from the PSBL.
This way, mail servers should be listed on the PSBL for a short time, while spam zombies could stay listed for long times. Because of this the PSBL helps stop spam, while not unduly punishing the users of real mail servers that got abused once.
There are plans to make the expiry algorithm smarter, so known mail servers are always for very short times and get removed quickly without a need for user intervention. Conversely, if there are no known mail servers inside a netblock with a lot of spam source IP addresses, the whole netblock could be listed automatically without needing to wait for spam from each and every IP address.
When changes are made, they'll be mentioned on the PSBL front page.