Issue #259 All About Email

Hi, {{first_name|friend}}. 👋

Welcome to Issue #259 of All About Email!

Last week, I followed up on Issue #256's finding that advanced AI adopters are 54% more likely to follow WCAG and 52% more likely to comply with the European Accessibility Act.

Now that I've read the full report, I wanted to see whether the extra context changes how I'd interpret those figures.

This week, I’m looking at email warm-up and a new blocklist from Validity called Heatwave.

🤔 If someone promises to “warm your domain and improve your deliverability”, what are they actually doing?

Let’s go! 👇

💡 Gradually increasing your sending volume can be a sensible part of moving platforms or introducing new sending infrastructure.

You send real emails to people who asked to receive them, monitor what happens, and adjust the pace.

Resend’s warmup guidance describes that process and distinguishes it from services that artificially boost engagement.

🤔 The confusion starts when both get sold under the same label. Synthetic warming involves controlled mailboxes exchanging messages and generating opens, clicks and replies to make a sender appear trusted.

Those opens, clicks, and replies are generated to influence reputation. They don’t tell you whether your actual subscribers want your emails.

That distinction matters when someone presents them as evidence that your deliverability is improving.

🤷‍♂️ If I’m paying someone to improve my deliverability, I’d want to understand which of those processes I’m paying for.

On 3 September 2026, Validity launched Heatwave, a domain blocklist targeting synthetic warming and associated cold-email infrastructure.

At launch, Validity said it had already listed more than one million domains exhibiting artificial-warming patterns.

💡 Andrew Bonar’s explanation on emailexpert highlights something useful: anyone can inspect the public lookup and read how the classifications work.

🤔 Could something you’re paying for to improve deliverability become another signal that your sending practices shouldn’t be trusted?

In his Spam Resource article, Al Iverson describes regularly hearing from senders who need help with deliverability after using warming or outreach services.

🫠 They expected an improvement. Instead, they arrived with inbox-placement problems and a domain reputation that, in his experience, was worse than when they started.

🧠 If a service claims to follow best practices, ask it to explain which practices it follows.

💡 The anti-abuse community had already warned about these practices. Heatwave adds another way to identify the domains involved.

Before we get carried away, there are a few distinctions worth making.

Those classifications tell you different things.

🚨 And a listing doesn’t establish that every mailbox provider will reject every email from that domain. Providers decide how to use the signal.

As Matt points out, we shouldn’t assume we know how heavily it will influence inbox placement.

There is, however, an important consequence in Validity’s listing policy:

💡 If your domain is listed, check which classification applies before deciding what to do next.

Maybe you don’t…

🤔 But does your agency? Your sales team? A subcontractor working for your outbound vendor?

Validity warns that warming activity can occur under a brand’s name without the company's knowledge, and that its lookup can surface related domains.

🚨 You might know exactly what happens inside your newsletter platform while having much less visibility into what another team or supplier is doing.

💡 Ask those teams and suppliers which domains they use on your behalf, what they send and whether any synthetic warming is involved.

If the lookup surfaces a domain you don’t recognise, first establish whether it’s connected to your organisation and who operates it.

An unfamiliar domain or listing should be checked before you conclude that your agency has done anything wrong.

✅ Three practical checks:

🚨 A clear result doesn’t mean every aspect of your sending is fine.

💡 Ask your vendor how it measures improvement, and whether those results come from your actual sends to subscribers.

We’ve spent plenty of time in this newsletter discussing engagement data that becomes unreliable due to privacy features, proxies, and automated systems.

Synthetic warming adds another problem: activity deliberately created to look like interest.

💡 I’m not against using a warming service, but before approving your next warmup service, ask it to explain what it does, who receives the messages and where the engagement comes from.

That’s it for this week, {{first_name|friend}}. 👋

Simon

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I hope you have a great week! 👋