Why does IP reputation still matter for some providers?

Despite the industry shift toward domain reputation, IP reputation remains influential for several categories of receivers.

Microsoft still weights IP reputation heavily in their SmartScreen filtering. Enterprise email gateways like Barracuda, Proofpoint, and Mimecast rely extensively on IP-based blocklists and reputation data.

Smaller ISPs and regional providers often lack the sophisticated machine learning systems that Google uses for domain analysis. They depend on simpler IP reputation checks because that infrastructure is proven and affordable.

Blocklists like Spamhaus, Barracuda, and SORBS operate at the IP level. Landing on these lists damages deliverability across all providers that query them, regardless of their domain reputation philosophy.

Some ports still inspect ships the old fashioned way. Until every harbor upgrades their systems, you need to keep both your vessel and your flag in good standing.