Why we don't do warmup (and never will)

Every few weeks a prospect asks us the same question: “Do you have warmup?” The answer is no. It will stay no. This post exists so we can link to it instead of retyping the reasoning.

What warmup actually is

A warmup tool connects your mailbox to a pool of other mailboxes. It then sends scripted emails between them — your domain sends a benign-looking thread, other pool members “reply”, “open”, and “mark as important”. The theory: the receiving provider sees positive engagement on your domain and raises your reputation.

That was a defensible hack in 2020. It's not a defensible product in 2026.

Why the model is breaking

1. Filters got better at detecting coordinated pools. A network of 5,000 domains exchanging structurally identical threads is statistically trivial to flag. Google, Microsoft and Yahoo all run ML classifiers on full inbound traffic — they see the coordination, you don't.
2. Apple MPP inflated opens everywhere. The primary metric warmup pools produced — opens — stopped meaning anything in 2021. The “open 100%” screenshots from warmup dashboards are telling you exactly nothing.
3. Gmail/Yahoo 2024 sender rules put alignment, one-click unsubscribe and complaint-rate thresholds at the centre of reputation. None of those are moved by warmup pools. A warmup tool that gets your domain through 2026 without those three fixed is lying about what is hurting you.
4. Reputation built on synthetic engagement is fragile. The day you stop paying the warmup bill, the synthetic traffic stops. Filters watch for that cliff. If your reputation was held up by the pool, you lose it in days.

The honest math

We've run blind placement tests on the output of three major warmup tools. Every one of them reports “95%+ inbox” internally. When we test the same domains against our seed network — mailboxes that are not in any warmup pool — the real placement is between 38% and 61%. The gap is not a rounding error. The dashboard is measuring the pool's own mailboxes agreeing with themselves.

Nobody ships a feature where the customer-facing number and the real number disagree by 50 points. We certainly won't.

What actually works instead

• Authentication on day one. SPF, aligned DKIM, and a real DMARC policy. No warmup compensates for missing these.
• Verified list. One bad list burns more reputation than a month of warmup can rebuild.
• Gradual ramp to real prospects. 20 → 40 → 80 → 150/day from your real ICP, not a pool. Real replies, real complaints, real reputation.
• Content that doesn't scream cold. Shorter, simpler, one link, zero tracking pixels if you can.
• Measurement outside the pool. Test placement from a seed network that is not part of your warmup tool. Otherwise you're grading your own homework.

The commercial honesty part

Warmup is a high-margin recurring SKU. Every vendor in this space has shipped one because the economics are irresistible — a pool costs the same regardless of how many customers join, but each customer pays monthly. We're aware of the money we're not making by leaving it on the table. We're also aware that the first wave of “warmup killed my domain” class-action stories is coming, and we'd rather not be named.

What we ship instead

1. Free placement tests across real mailboxes — the honest number.
2. Pre-send draft analysis — stop-words, domain auth, link intel, AI human-perception score — before you burn a real send.
3. API + MCP server so you can run tests in CI and agent workflows.
4. A polite no when you ask us to bolt on synthetic engagement.

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