> No, it is not a SPOF. If the PS goes down, traffic keeps flowing as normal; it just doesn’t get spamchecked. They do not give a “go/no go instruction to the l

> No, it is not a SPOF. If the PS goes down, traffic keeps flowing as normal; it just doesn’t get spamchecked. They do not give a “go/no go instruction to the larger network”; they are something which servers can check against. That is still a failure (to spam check), even if it is not a failure to deliver the messages altogether. It may also end up being a vulnerability. For example, the attackers might do a some sort of flood attack on the policy server, and then get the abuse through.