Validity Heatwave Blocklist Targets Synthetic Domain Warming at Scale
The Development
Validity launched Heatwave on September 3, a purpose-built blocklist targeting artificial domain warming — the practice of using fake accounts to generate synthetic opens, clicks, and replies that trick mailbox providers into trusting a sender. Drawing on the Validity Intelligence Network, Heatwave has already listed over 1 million domains displaying warming behavior. The signal is integrated directly into Validity's existing DNS reputation zones, meaning partners already consuming Validity reputation data receive it without additional integration. Confirmed users include Comcast, Proofpoint, Spamhaus, SURBL, and beehiiv, with additional mailbox providers and ESPs in evaluation. Domains can be queried publicly at lookup.validity.tools.
Our Take
Domain warming services proliferated precisely because the risk of detection was low and the deliverability payoff was real. Heatwave changes the enforcement calculus. With Comcast, Proofpoint, and Spamhaus already consuming the signal, the coverage is significant enough to make synthetic warming genuinely dangerous rather than merely against policy. The more consequential detail is the third-party exposure risk: because warming often runs through subcontracted vendors operating several layers from the brand, marketing teams can find their primary domain flagged through infrastructure they never authorized. That is a deliverability crisis with a reputational dimension, and most enterprise email teams have no audit process to catch it.
What Changed
For the first time, mailbox providers and ESPs have a dedicated, cross-ecosystem signal that identifies synthetically constructed sender reputation — distinct from general spam or abuse signals. Infrastructure built on fake engagement can now be correlated across independent data sources before it ever reaches the inbox.
Marketing Impact
Email marketing and marketing operations teams face immediate exposure risk if any portion of their vendor stack includes third-party warm-up services. Deliverability infrastructure audits — specifically mapping every domain and subdomain associated with outbound send activity — become a compliance function, not just a hygiene task.
Competitive Implication
Legitimate permission-based email programs gain a structural advantage as synthetically warmed competitors face filtering penalties at scale. Cold outreach vendors and growth agencies relying on warming services face existential pressure as ESP enforcement, now backed by Heatwave data, becomes unavoidable.
Strategic Outlook
ESP enforcement actions against customers with Heatwave-flagged domains will accelerate through Q4 2026 as providers complete evaluation and move from signal consumption to policy triggers. Brands will face account suspensions at their ESP before their own teams identify the underlying cause.
The Exploit
Action Item
Email operations leads at any brand using outbound cold prospecting should run their primary and associated domains through lookup.validity.tools immediately, then require written confirmation from every send-side vendor that no warming services are embedded in their delivery stack.