As far as I am concerned the PBL is a tool to facilitate net neutrality violations, not by ISPs, but by e. mail service providers.*
Another effort by anti-spam people to encourage network neutrality violations is the SUBMISSION port, port 587 as opposed to port 25, for the authenticated submission of mail by MUAs. As far as I can tell, the only possible utility of this split is to make it more politically feasible for ISPs to block port 25 out, i.e. to facilitate network neutrality violations. As such I do not view the SUBMISSION port RFC well.
(*Some people argue that PBL networks have no business sending mail because they have dynamic IPs. This is false; there are PBL-listed networks which assign static IPs, and it is at any rate a moot point. No specification requires that MTAs for domain outgoing mail and MXs (that is, MTAs for incoming mail) be one and the same, and there is only a technical need for the latter to have fixed IPs.)
Another effort by anti-spam people to encourage network neutrality violations is the SUBMISSION port, port 587 as opposed to port 25, for the authenticated submission of mail by MUAs. As far as I can tell, the only possible utility of this split is to make it more politically feasible for ISPs to block port 25 out, i.e. to facilitate network neutrality violations. As such I do not view the SUBMISSION port RFC well.
(*Some people argue that PBL networks have no business sending mail because they have dynamic IPs. This is false; there are PBL-listed networks which assign static IPs, and it is at any rate a moot point. No specification requires that MTAs for domain outgoing mail and MXs (that is, MTAs for incoming mail) be one and the same, and there is only a technical need for the latter to have fixed IPs.)
See also my site https://violations.devever.net/w/Violation_Type:Rejects_Vali...