Read the Docs + GitHub: getting failure-only build alerts without the success noise

Goal

I have a Read the Docs project connected to a GitHub repository through the native webhook integration, so every push and pull request triggers a documentation build. Email notifications are enabled under Settings → Notifications, but that toggle appears to cover all build outcomes, so successful builds generate the same volume of mail as failures. My goal is to alert only when a build breaks, without routing every routine success through my inbox.

Constraints and uncertainty

The dashboard does not seem to expose a failure-only option, while the API documentation hints that webhook notification behavior may be configurable per endpoint. It is unclear whether that parameter is available on the free community hosting tier or restricted to Read the Docs for Business. I would prefer to avoid an external filter (GitHub Actions, Zapier, or a relay script) because that adds latency and a failure point that could silently drop a critical alert. Assume a recent stable Read the Docs deployment; behavior may differ between plans, so answers should note which tier they apply to.

Questions

• Is there a supported way, via the API or otherwise, to configure the GitHub webhook integration so email notifications fire only on failed builds?
• If failure-only alerting requires the API, is that endpoint available on the free tier, and does it apply to the auto-created GitHub webhook or only to manually configured ones?
• Absent a native option, what is the lowest-noise pattern teams use that still guarantees a missed external service cannot swallow a failure alert?