The Dark Side of Email Deliverability: What Validity’s Heatwave Blocklist Means for Senders

If you use a service that promises to improve your email reputation through automated engagement, review how it works. Validity’s new Heatwave blocklist targets synthetic reputation warming, making those shortcuts worth a closer look. Validity’s announcement

Think about the temptation of the dark side in Star Wars: a shortcut to the power you want.

Now imagine your emails are landing in spam. Fewer people are seeing your offers. You’re feeling pressure to turn things around.

Someone offers a solution: connect your mailbox, let their system “warm up” your domain, and watch your reputation improve.

I understand the appeal. When email revenue is slipping, a quick fix sounds good.

But before you connect that service, ask one question:

How is that trust being earned?

What is Validity’s Heatwave blocklist?

Validity launched Heatwave on September 3, 2026, and reported more than one million listed domains at launch. It gives email providers and security services another signal for identifying reputation manipulation. Validity’s announcement

Heatwave focuses on the sending domain, not the IP address.

Its target is synthetic reputation warming: automated exchanges between controlled mailboxes intended to manufacture a positive sending reputation before outreach begins. Signals come through the Validity Intelligence Network. Heatwave listing criteria

The concern is straightforward. Manufactured activity does not demonstrate that your customers want your emails.

Is warming your email domain a bad thing?

Gradually increasing legitimate sending volume is an established practice. Google recommends starting with low volume to engaged users, increasing slowly, and monitoring delivery responses and spam reports. Google’s sender guidelines

That gives you a practical question to ask any provider offering warm-up:

Are we gradually sending to people who asked to hear from us, or paying a network to simulate interest?

A gradual sending plan gives you time to observe how your audience responds. A service that manufactures engagement is trying to create the appearance of that response.

I would require a clear explanation of the method before approving the service. A better-looking dashboard would not be enough for me.

Why does a domain get listed?

Heatwave distinguishes between observed warming, subsequent cold outreach, and related domains that have not yet been observed sending.

A listing does not mean every listed domain has already sent warming messages or cold outreach. The stage matters when interpreting the result. Heatwave listing criteria

Heatwave evaluates factors including domain age, sending infrastructure, and message characteristics. Domains exceeding its threshold are listed automatically, and all listings are subject to manual review.

The displayed listing score is a relative band from 1–100 compared with recent listings. It can change over time and does not determine whether the domain gets listed. A score of 0 means a manual listing.

The observation age indicates how long the domain has been known as a synthetic sender since its first warming observation. It is not the domain’s registration age. Heatwave listing criteria

Why this matters even if you never bought a warming tool

Validity says synthetic warming can happen through subcontractors without a brand’s knowledge. Its lookup can also surface related domains associated with this activity. Validity’s announcement

My recommendation: ask your agency or outreach provider to document what is running on your behalf.

Start with these questions:

• Which domains and mailboxes are you using?
• Are any tools generating automated engagement?
• Have you connected our mailboxes to a warming network?
• Do subcontractors manage any part of our sending?
• Can you explain exactly how your process builds reputation?

“We handle deliverability” is not a sufficient answer.

Does a Heatwave listing mean everyone blocks your email?

Validity describes Heatwave as an additional signal for filtering and abuse detection. Its announcement names organizations using or evaluating it, rather than confirming universal blocking. Validity’s announcement

Does Gmail or Microsoft automatically reject messages because of a Heatwave listing? I cannot confirm this.

Treat a listing as a reason to investigate. Review the domain, its listing stage, the activity involved, and your delivery logs before deciding what it means for your business.

What I recommend doing now

Check your domains. Start with Validity’s Heatwave lookup. Review any related domains it surfaces and determine whether they belong to your organization or its vendors.

Question the method. Ask providers to explain how their warm-up works. If the process manufactures engagement, my recommendation is to stop that activity and investigate the affected infrastructure.

Review the fundamentals. Check authentication, list sources, recipient complaints, and sending volume. Google’s guidance emphasizes authentication, wanted email, gradual volume increases, and easy unsubscribing. Google’s sender guidelines

Respond to warning signs. Google recommends monitoring server responses and spam rates as volume grows, and reducing volume when messages begin bouncing or being deferred. Google’s sender guidelines

The EmailSmart point of view

My advice is to resist any service whose main promise is making your reputation look better without improving the experience of the people receiving your emails.

For permission-based marketing, our operating principle is simple: permission gets someone onto your list. Continuing to earn their interest should guide what you send next.

If your audience has stopped responding, investigate why.

Review what you promised when they subscribed. Look at what you’re sending, how often you’re sending it, and whether it still serves their needs.

Put that work ahead of manufactured activity.

Don’t succumb to the power of the dark side. Build an email program your audience actually wants.

Want help reviewing your email setup? Start with a free EmailSmart scan.