---
title: "Bounce Diagnosis Claude Skill: List or Sender?"
description: "A Claude skill that reads pasted bounces and headers, splits them into list problems and sender problems, and says what to do with each. No API key."
url: https://warminboxes.com/skills/bounce-diagnosis
breadcrumb: "Home > Claude Skills > Bounce Diagnosis"
---
Claude skill

# Bounce Diagnosis

What do these bounces mean, and is it the list or me?

A list problem and a sender problem look the same on a dashboard and need opposite answers: one is cleaned, the other is rested. Paste the bounces or the headers and this sorts them code by code before anything else, so nobody pauses a healthy domain over a bad list, or keeps sending from a tenant Microsoft has stopped accepting.

## What it runs

- **Bounce codes** — Every NDR classified: bad address, policy or reputation refusal, tenant-level block, or throttling

- **Microsoft headers** — SCL, BCL and the verdict, for “why is Outlook junking this?”

- **Full headers** — Authentication results and the route the message actually took

- **The domain the bounces name** — Reputation signals and blocklists, checked rather than assumed

- **A sample of bounced addresses** — Verified again, to answer “is it the list?” with evidence

## What you get back

- The split first: how many bounces are the list and how many are the sender

- Each code with its count and what it means, including where Microsoft has not documented one

- The operator rule that applies: clean the list, or stop cold sending entirely and rest, then ramp back

- One next action, and new infrastructure only when the bounces name the domain or tenant and a rest has failed

## Install it

Best installed with the plugin, which also connects WarmInboxes Free MCP, the tools this skill runs. On its own it is one file that falls back to the free WarmInboxes API, so there is no key and nothing to sign up for.

 /plugin marketplace add Huz-ai-fa/warminboxes-claude-skills
/plugin install warminboxes@warminboxes

Or this one skill on its own:

 mkdir -p ~/.claude/skills/bounce-diagnosis
curl -sL https://raw.githubusercontent.com/Huz-ai-fa/warminboxes-claude-skills/main/bounce-diagnosis/SKILL.md -o ~/.claude/skills/bounce-diagnosis/SKILL.md

[View it on GitHub →](https://github.com/Huz-ai-fa/warminboxes-claude-skills/tree/main/bounce-diagnosis)

## Then just ask

You do not name the skill. Its description tells Claude when it applies.

- "Here are 40 bounces from yesterday, what is going on?"

- "We are getting 550 5.7.708 from Microsoft, is the tenant dead?"

- "Is a 6% bounce rate a list problem or a domain problem?"

Every answer cites the check behind it, so anything Claude tells you can be re-run by hand. A clean result is reported clean, with nothing to buy.

[All Claude skills →](https://warminboxes.com/skills)

## Do it by hand

The same checks as free tools in a browser.

- [Bounce Analyzer](https://warminboxes.com/bounce-analyzer)

- [Header Analyzer](https://warminboxes.com/header-analyzer)

- [Email Verifier](https://warminboxes.com/email-verifier)

## The other skills

One page each.

- [Inbox Checker](https://warminboxes.com/skills/inbox-checker) — Is this domain burned?

- [Domain Audit](https://warminboxes.com/skills/domain-audit) — Is this domain set up correctly to send from?

- [List Segmentation](https://warminboxes.com/skills/list-segmentation) — Who hosts the people on this list?

- [Infrastructure Planner](https://warminboxes.com/skills/infrastructure-planner) — How many mailboxes do I need, and what does it cost?

- [Cold Email Copy](https://warminboxes.com/skills/cold-email-copy) — Is this email going to land in spam?

- [Lead Lists](https://warminboxes.com/skills/lead-lists) — Is this list ready to send to?

- [Warm Rotation](https://warminboxes.com/skills/warm-rotation) — How do I make my inboxes last longer?

- [Cold Email Playbook](https://warminboxes.com/skills/cold-email-playbook) — Why did my replies drop, and what do I do?

- [Infrastructure API](https://warminboxes.com/skills/infrastructure-api) — How do I connect my WarmInboxes account to Claude?