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.
npx skills add ericrisco/rsc-harness --skill email-deliverabilitygit clone --depth 1 https://github.com/ericrisco/rsc-harnessWrote 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.
[](https://agentmods.dev/skills/ericrisco/rsc-harness/email-deliverability)<a href="https://agentmods.dev/skills/ericrisco/rsc-harness/email-deliverability"><img src="https://agentmods.dev/badge/skills/ericrisco/rsc-harness/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.
<a href="https://agentmods.dev/skills/ericrisco/rsc-harness/email-deliverability"><img src="https://agentmods.dev/badge/skills/ericrisco/rsc-harness/email-deliverability.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00084 | $0.02339 |
| Opus 5 | $0.00042 | $0.01170 |
| Sonnet 5 | $0.00017 | $0.00468 |
| Haiku 4.5 | $0.00008 | $0.00234 |
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 5d 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.
How it starts
The opening of the file, as written. The whole thing — 149 lines — stays where its author put it; the contents beside it link to each section on GitHub.
email-deliverability — make mail authenticate and land in the inbox
This skill owns one layer: why mail you already send gets filtered, deferred, or rejected, and the DNS + reputation work that fixes it. It starts where the send technically succeeds but the message never reaches the inbox.
The lever is almost never the sending code. It is three DNS records that must align, a complaint rate you must hold down, and a reputation you build slowly and lose fast. Treat this as ops on a domain, not a code change.
Not this skill
- Sending the mail at all — provider SDK,
sendEmail()seam, templates, retries, batch caps, bounce/complaint webhooks →../email-connector/SKILL.md. That skill feeds the suppression list; this one explains the reputation it protects. - Subject lines, open/click optimization, list growth →
newsletter. - Outbound prospecting sequences, lead lists →
cold-outreach(deliverability is a constraint on it, not the same job). - Consent, lawful basis, retention of the address list →
gdpr-privacyanddata-policy. Unsubscribe mechanics live here; consent law does not. - Handling the DKIM private key and provider API secrets →
../secure-coding/SKILL.md.
The three records that must align
SPF, DKIM, and DMARC are not three ways to do the same thing. DMARC is the
policy; it passes only when SPF or DKIM both authenticate and align with
the visible From: domain. Most "SPF is set but DMARC fails" tickets are an
alignment miss, not a missing record.
| Record | What it asserts | Common break |
|---|---|---|
| SPF (TXT) | This IP/host is allowed to send for the domain | Lists the provider but the Return-Path is a different domain → no alignment |
| DKIM (TXT) | This message body+headers are signed by a key the domain published | Provider signs with provider.net, not your domain → no alignment; or a deprecated 1024-bit key (publish 2048-bit, rotate periodically) |
DMARC (TXT at _dmarc) |
What to do when neither aligns, plus where to send reports | Policy left at p=none forever; never tightened |
What ships with it
3 files 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.
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.
- 5d ago First seen · 149 lines · 84 tokens per session scan A cd108ba466a5
email-deliverability is a skill published in the GitHub repository ericrisco/rsc-harness (74 stars, last pushed yesterday), licensed MIT. It adds 84 tokens to every session and 2,339 once invoked, about $0.0004 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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