What is email-deliverability?

A troubleshooting guide for email authentication and delivery problems involving SPF, DKIM, DMARC, DNS, Google Workspace, and Namecheap Private Email.

Checking mail-related DNS records, setting up domain authentication, diagnosing bounces, and fixing common provider-specific email problems.

It helps identify configuration errors that can cause messages to bounce or land in spam.

email-deliverability — Skill for Claude Code and Codex by S3YED

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add S3YED/appie-kit --skill email-deliverability

Clone the repo

git clone --depth 1 https://github.com/S3YED/appie-kit

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/s3yed/appie-kit/email-deliverability/github.svg)](https://agentmods.dev/skills/s3yed/appie-kit/email-deliverability)

Your own site

<a href="https://agentmods.dev/skills/s3yed/appie-kit/email-deliverability"><img src="https://agentmods.dev/badge/skills/s3yed/appie-kit/email-deliverability/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/s3yed/appie-kit/email-deliverability"><img src="https://agentmods.dev/badge/skills/s3yed/appie-kit/email-deliverability.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 660 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00039	$0.00660
Opus 5	$0.00019	$0.00330
Sonnet 5	$0.00008	$0.00132
Haiku 4.5	$0.00004	$0.00066

Measured 9d ago against content hash 20d648e5d211, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

email-deliverability scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/devops/email-deliverability/SKILL.md · 80 lines

How it starts

The opening of the file, as written. The whole thing — 80 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Email Deliverability

Diagnose and fix email authentication (SPF/DKIM/DMARC) for Weblyfe client domains. Most common scenario: Namecheap Private Email receiving or Google Workspace sending.

Triggers

"Email gaat naar spam"
"Mail komt niet aan bij [client]"
"Address not found" bounce van Namecheap
Nieuwe domein mail setup

Quick Diagnostic

# Check all three for any domain
dig DOMAIN TXT +short | grep spf    # SPF
dig SELECTOR._domainkey.DOMAIN TXT +short  # DKIM
dig _dmarc.DOMAIN TXT +short        # DMARC

Common Patterns

Google Workspace Sending → Namecheap Private Email Receiving

Symptom: 554 5.1.1 Recipient address rejected: undeliverable address (JFE030050)

Root cause: Namecheap is strict on SPF. If the sending domain has no SPF, Namecheap bounces with "address not found" even though the mailbox exists.

Fix: Add SPF to sending domain:

v=spf1 include:_spf.google.com ~all

Namecheap Private Email Sending → Anywhere

SPF: Auto-configured when you activate Private Email:

v=spf1 include:spf.privateemail.com ~all

DKIM: Must be manually enabled in Namecheap dashboard:

Private Email → Manage → Email Security → DKIM → Generate
Copy Host + DNS Record values
Add as TXT record in DNS
Selector is privateemail (NOT default)

DMARC: Add TXT record:

Host: _dmarc
Value: v=DMARC1; p=none; rua=mailto:info@DOMAIN

DNSSEC Warning

Namecheap defaults to DNSSEC on. If DNS is managed elsewhere (Cloudflare, DO), DNSSEC must be disabled at Namecheap or records won't resolve.

Verification

After setup, send a test email and check headers for:

spf=pass
dkim=pass
dmarc=pass

Pitfalls

Namecheap DKIM selector is privateemail, not default. Dig for privateemail._domainkey.DOMAIN.
Missing SPF causes "address not found" on Namecheap, not "SPF failed". The error is misleading.
DMARC p=none is monitor-only. Start here, verify for 2 weeks, then tighten.
DKIM record contains the public key — no separate public key upload needed.
Only ONE SPF record per domain. Multiple TXT records starting with v=spf1 breaks validation.

Read the full file on GitHub · 80 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

references/namecheap-jfe030050.md 1.3 KB

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

9d ago First seen · 80 lines · 39 tokens per session scan A 20d648e5d211

Subscribe to this mod's changes

email-deliverability is a skill published in the GitHub repository S3YED/appie-kit (9 stars, last pushed 17d ago), licensed MIT. It adds 39 tokens to every session and 660 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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