---
title: "Warmup Services Harm Your Deliverability"
description: "Warmup services that simulate email engagement harm deliverability because inbox providers detect the pattern and tighten filtering, causing reputation decline that makes recovery harder. Validity’s new Heatwave blocklist identifies domains warmed through synthetic engagement, using signals from its Intelligence Network to automatically list domains crossing a threshold, and over 1.2 million domains have already been listed. The signal is shared with providers including Comcast, Proofpoint, Spamhaus, and SURBL, potentially damaging domain reputation with these providers. A domain on Heatwave receives a permanent record, and even if the domain stops cold outreach, the warming listing stays, making recovery difficult or impossible. Legitimate senders should verify their domain at lookup.validity.tools, obtain proper consent, and increase volume gradually through real engagement, as the domain warms itself through real engagement and there is no shortcut to trust; warmup activity may also run through agencies without the sender’s knowledge."
---

# Warmup Services Harm Your Deliverability

[Resend](https://yomu.fyi/company/resend) · Phil Nash · Sep 30, 2026

**Type:** Explainer

## Summary

Warmup services that simulate email engagement harm deliverability because inbox providers detect the pattern and tighten filtering, causing reputation decline that makes recovery harder. Validity’s new Heatwave blocklist identifies domains warmed through synthetic engagement, using signals from its Intelligence Network to automatically list domains crossing a threshold, and over 1.2 million domains have already been listed. The signal is shared with providers including Comcast, Proofpoint, Spamhaus, and SURBL, potentially damaging domain reputation with these providers. A domain on Heatwave receives a permanent record, and even if the domain stops cold outreach, the warming listing stays, making recovery difficult or impossible. Legitimate senders should verify their domain at lookup.validity.tools, obtain proper consent, and increase volume gradually through real engagement, as the domain warms itself through real engagement and there is no shortcut to trust; warmup activity may also run through agencies without the sender’s knowledge.

## Context

Email senders have used warmup services to simulate engagement and improve deliverability, but inbox providers detect this pattern. Validity’s new Heatwave blocklist now identifies domains warmed through synthetic engagement, making the practice riskier.

## Approach / What changed

Verify your domain, obtain proper consent, and increase email volume gradually through real engagement rather than using warmup services.

## Takeaways

- Warmup services that simulate email engagement harm deliverability because inbox providers detect the pattern and tighten filtering, causing reputation decline that makes recovery harder.
- Validity’s Heatwave blocklist permanently lists domains that cross a threshold for synthetic warming, and the signal is shared with providers like Comcast, Proofpoint, Spamhaus, and SURBL.
- Legitimate senders should verify their domain, obtain proper consent, and increase volume gradually through real engagement, as there is no shortcut to trust.

## FAQ

### What is Heatwave?

Heatwave is a blocklist from Validity that identifies domains warmed through synthetic engagement. It uses signals from Validity's Intelligence Network to automatically list domains crossing a threshold, and over 1.2 million domains have already been listed.

### How can I check if my domain is on Heatwave?

You can search your domain at lookup.validity.tools. The results may include related domains you didn't know existed.

### Can I remove my domain from Heatwave?

Once your domain crosses Heatwave's threshold, its position on the blocklist is permanent. However, if your domain is listed for cold outreach, that status can be removed once the outreach stops, but the warming listing stays.

**Tags:** [Deliverability](https://yomu.fyi/topic/deliverability), [Email](https://yomu.fyi/topic/email), [Email Marketing](https://yomu.fyi/topic/email-marketing)

- Source: [Resend](https://resend.com/blog/avoid-warmup-services)
- Source URL: https://resend.com/blog/avoid-warmup-services
- Ingested by Yomu: 2026-09-28T12:00:15.850Z

[Read original post](https://resend.com/blog/avoid-warmup-services)