Spamhaus PBL

Spamhuas 新推出的 DNSBL

The Policy Block List

The Spamhaus PBL is a DNSBL database of end-user IP address ranges which should not be delivering unauthenticated SMTP email to any Internet mail server except those provided for specifically by an ISP for that customer's use. The PBL helps networks enforce their Acceptable Use Policy for dynamic and non-MTA customer IP ranges.

PBL IP address ranges are added and maintained by each network participating in the PBL project, working in conjunction with the Spamhaus PBL team, to help apply their outbound email policies. Additional IP address ranges may be added and maintained by the Spamhaus PBL Team, particularly for networks which are not participating themselves, and where spam, rDNS and server patterns
are consistent with end-user IP space which typically contain high concentrations of "botnet zombies", a major source of spam.

A list of participating networks will be available soon. Spamhaus encourages all dialup, DSL and cable modem providers to participate and submit their own PBL ranges.

這是 ISP 自動參與的 DNSBL，ISP 指定那些 ip range 不是用她們指定的 SMTP server 寄信，而真接 email direct to MX.
但我的問題是: 為何這些 ISP 不 block 了 outgoing port 25，正如香港的ISP Netvigator那般，根本她們的用戶就不能 direct to mx!!