---
title: Synthetic engagement is now a blocklistable offence. What Validity's Heatwave means for anybody using a warm-up tool
description: Validity's Heatwave blocklist targets synthetic email engagement and warm-up tools. What counts as artificial warming, how you might be doing it, and what to do instead.
---

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 10/2026

# Synthetic engagement is now a blocklistable offence. What Validity's Heatwave means for anybody using a warm-up tool

![Picture of Beth O'Malley](https://app.hubspot.com/settings/avatar/2761c9d87ba551994b382ed8415ad538) [Beth O'Malley](https://weareastral.co.uk/thevault/author/beth-omalley)

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On 3 September 2026, Validity launched a blocklist called Heatwave, aimed specifically at domains that manufacture engagement to warm up a sending reputation.

At launch it had already identified more than a million domains displaying artificial-warming behaviour. It is served through Validity's existing DNS reputation feeds, and the announcement named Comcast, Proofpoint, Spamhaus and SURBL among the organisations using or evaluating it.

I have been saying for a while that automated warm-up tools were becoming a liability rather than a shortcut, and that businesses would damage themselves taking AI-shaped shortcuts in email, and here we are: the first piece of hard infrastructure built to catch exactly that, and it will not be the last.

PSA: I use warm-up tools, with the right strategy and being VERY careful, they can temporarily help your deliverability if it's REALLY, REALLY bad. 

 

## Before you dig in, why don't you get access to RE:markable

  RE:markable is the weekly email about emails. Dropping the latest email marketing news, updates, insights, free resources, upcoming masterclasses, webinars, and of course, a little inbox mischief. 

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# The practice

## What synthetic engagement means

Validity describes synthetic warming as exchanges that manufacture engagement through controlled accounts, including simulated opens, clicks and replies.

Which in practice means one of a few arrangements.

- Warm-up networks. Your new domain sends to a pool of mailboxes controlled by the tool or by other customers of it. Those mailboxes open your email, click something, reply, and move it out of spam, generating a stream of positive signals that no human produced.
- Seed pools that engage on a schedule. Automated accounts behaving like enthusiastic subscribers, at volumes and consistencies no real audience produces.
- Reciprocal engagement arrangements. Senders agreeing to engage with each other's mail, which is the same mechanism with a friendlier name on it.

The logic has always been superficially reasonable. Providers reward engagement, a new domain has none, so manufacture some until the real audience arrives. The problem is that the behaviour is detectable, because real engagement is messy and synthetic engagement is not.

 

## Why it was always going to be caught:

*Real audiences are inconsistent. They open at odd hours, ignore things for weeks, click occasionally, and behave differently from each other.*

*A pool of accounts engineered to engage produces a pattern that is too regular, too mutual and too clean. Pattern detection is exactly the thing filtering systems are good at, and the behaviour is distinctive once you go looking for it.*

![Email health check](https://weareastral.co.uk/hs-fs/hubfs/Email%20health%20check%20(1200%20x%20800%20px)%20(1).png?width=1200&height=800&name=Email%20health%20check%20(1200%20x%20800%20px)%20(1).png)

## Free Email Marketing Health Check

### Audit your entire ecosystem in under 30 minutes

Answer a set of straightforward questions across every area of email marketing and get a personalised score, traffic-light priorities, and clear actions and improvements you can make today.

[Take the Health Check →](https://www.emaildeliverabilitycheck.co.uk/)

# Without realising

## How you might be generating synthetic signals right now

Plenty of businesses on this list did not set out to fake anything, which is the part worth being careful about.

- You bought a warm-up tool and left it running. The most common route. Somebody enabled it during a migration or a domain change eighteen months ago, nobody switched it off, and it has been generating fake engagement ever since.
- Your cold outreach platform includes warming as a feature. Several do, switched on by default, described as inbox warming or deliverability optimisation in the interface. You may be using it without ever having chosen it.
- An agency or consultant set it up for you. And did not mention it, because at the time it was considered standard practice.
- You are on a shared pool somebody else is abusing. Sending-platform IP ranges hosting AI-scaled sequences have been blocklisted faster this year, and several 2026 incidents took entire pools down for days. You do not have to be the one misbehaving.
- Internal seed lists that engage on every send. A grey area rather than an offence. A handful of colleagues checking rendering is testing. Forty internal accounts opening and clicking every campaign to prop up the numbers is closer to the behaviour being detected.

### How to find out

1. Ask what warming your platform does, in writing. Specifically whether it uses a network of accounts, and what those accounts do with your mail. A vague answer is an answer.
2. Check whether a warm-up tool is still connected. Including anything enabled for a migration, a new domain or a cold outreach campaign that has since ended.
3. Look at your own engagement data for suspicious cleanliness. Unusually consistent open and click behaviour from a cluster of addresses you cannot account for, at regular intervals, is worth investigating.
4. Check your domains against the reputation feeds. Including the new signal, since it is served through Validity’s existing zones rather than as a separate product you have to buy.

 

# The consequences

## What a listing would do to you

- The filtering consequence is immediate. A blocklist served through widely-used reputation feeds affects placement wherever those feeds are consumed, and the named partners cover a meaningful share of the mail you send.
- It attaches to the domain. Which follows you across platforms, so changing ESP does not escape it, and the domain carrying it may also be carrying your transactional mail.
- The record persists. Validity's listing policy keeps an accurate warming observation on record. Delisting is not the same as the observation never having happened.
- And it is a credibility problem as well as a technical one. Explaining to a board that your email stopped arriving because a tool you were paying for was faking engagement on your behalf is not a comfortable meeting.

 

## The asymmetry:

*Synthetic warming buys you a few weeks of artificially good signals at the start of a domain's life.*

*A listing costs you placement across providers, attaches to the asset you cannot easily replace, and leaves a record. It was never a good trade and now the downside is explicit.*

# Instead

## How to warm a domain without manufacturing anything

1. Start with the people most likely to engage. Your most engaged subscribers, in small volumes. Real humans producing real signals, which is the only kind that builds a reputation worth having.
2. Increase in steps across weeks, not days. Four to eight weeks minimum, longer for large programmes. The shape matters more than the numbers: steady, predictable, never doubling overnight.
3. Watch complaints and bounces at every step. And hold at the current volume rather than pushing on whenever either moves the wrong way.
4. Keep cadence consistent. A domain sending regularly looks established. One sending in bursts looks like software, which is the impression you are trying to avoid.
5. Run the old domain in parallel. So you are not forced to push the new one faster than it can go.
6. Give it the time it needs. The plain answer is that warming is slow, there is no shortcut, and every product sold as one has eventually stopped working or started costing people more than it saved.

 

## The conclusion

A small piece of news with a larger point attached to it.

Every shortcut in email deliverability has the same lifecycle. It works, it gets productised, enough people use it that the pattern becomes obvious, detection gets built, and the people still using it are worse off than if they had never started. Warm-up tools have now reached the detection stage, publicly, with named partners consuming the signal.

And the broader version is the thing I keep saying about AI in email. The risk is not that a filter detects that something was automated. It is that automation produces patterns, patterns get recognised, and whatever advantage existed disappears while the evidence of having used it remains.

Reputation is earned by sending mail people want. It is slow, it is unglamorous, and it is the only version that cannot be detected and penalised, because there is nothing to detect.

 

## A quick win:

*Find out, today, whether anything in your stack is doing automated warming on your behalf. Ask your platform, your agency and whoever set up your last new domain.*

*A surprising number of businesses discover something switched on that nobody remembers choosing, and switching it off costs nothing.*

![Getting email deliverability right What to know & track (1080 x 900 px) (1)](https://weareastral.co.uk/hs-fs/hubfs/Copy%20of%20Getting%20email%20deliverability%20right%20What%20to%20know%20%26%20track%20(1080%20x%20900%20px)%20(1).png?width=1080&height=900&name=Copy%20of%20Getting%20email%20deliverability%20right%20What%20to%20know%20%26%20track%20(1080%20x%20900%20px)%20(1).png)

## There is no shortcut, which is good news if you do the work

Every tool sold as a deliverability shortcut eventually stops working. The businesses that come through fine are the ones who understood the mechanism rather than buying a product that promised to handle it.

 

My free 60 minute Email Deliverability Training covers reputation, warming, the signals that build and decay it and what normal looks like. The Email Deliverability Certification Programme takes you through the full audit process.

[Join the free deliverability training →](https://weareastral.co.uk/free-email-deliverability-training)

### Further reading from The Vault:

- [How to Run Cold Email Without Destroying Your Domain](https://weareastral.co.uk/thevault/how-to-run-cold-email-without-destroying-your-domain.-and-what-to-build-before-the-window-closes)
- [Changing Your Email Sending Domain](https://weareastral.co.uk/thevault/changing-your-email-sending-domain-what-it-does-to-your-sender-reputation-and-how-to-do-it-safely)
- [The Future of Email Marketing](https://weareastral.co.uk/thevault/the-future-of-email-marketing-what-changed-in-2026-what-did-not-and-what-happens-next)
- [Email Behaving Badly: Why Compliance Will Not Save Your Deliverability](https://weareastral.co.uk/thevault/email-behaving-badly-why-compliance-will-not-save-your-deliverability)
- [How to Know Your Sender Reputation](https://weareastral.co.uk/thevault/how-to-know-your-sender-reputation.-why-you-cannot-look-it-up-any-more-and-how-to-work-it-out-instead)
- [The State of Email Deliverability in 2026](https://weareastral.co.uk/thevault/the-state-of-email-deliverability-in-2026.-and-what-i-think-happens-in-2027)

  

## Like this blog? You'll love RE:markable

 RE:markable is the weekly email about emails. Dropping the latest email marketing news, updates, insights, free resources, upcoming masterclasses, webinars, and of course, a little inbox mischief.

 Subscribe to RE:markable

## Email, CRM and HubSpot Support

I help marketers and businesses **globally** improve, design and fix their email, CRM, and HubSpot ecosystems, from strategy through to execution.

**My services include:**

- Email marketing strategy, audits, training, workshops, and consultancy
- CRM strategy and enablement
- Full HubSpot implementations, optimisation and onboarding through my agency

If you’re looking for experienced external support (and lots of enjoyment along the way), this is where to start.

[Work with Beth](https://weareastral.co.uk/work-with-beth)

 

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[Email Marketing](https://weareastral.co.uk/thevault/tag/email-marketing), [Marketing Strategy](https://weareastral.co.uk/thevault/tag/marketing-strategy)

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