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 sendx/email-skills --skill email-deliverability-expert-skillgit clone --depth 1 https://github.com/sendx/email-skillsWrote 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/sendx/email-skills/email-deliverability-expert-skill)<a href="https://agentmods.dev/skills/sendx/email-skills/email-deliverability-expert-skill"><img src="https://agentmods.dev/badge/skills/sendx/email-skills/email-deliverability-expert-skill/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/sendx/email-skills/email-deliverability-expert-skill"><img src="https://agentmods.dev/badge/skills/sendx/email-skills/email-deliverability-expert-skill.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00189 | $0.05176 |
| Opus 5 | $0.00095 | $0.02588 |
| Sonnet 5 | $0.00038 | $0.01035 |
| Haiku 4.5 | $0.00019 | $0.00518 |
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 11d 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 — 363 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Email Deliverability: Audit, Diagnosis & Fix
Your Setup — Fill These In for Better Results
This skill gives generic advice by default. Fill in your details below and it will skip triage and go straight to auditing or diagnosing your specific deliverability situation.
- Sending domain(s): [e.g., mail.yourcompany.com]
- ESP / sending platform: [e.g., SendX, Mailchimp, custom MTA]
- Monthly send volume: [e.g., 500,000]
- IP type: [shared / dedicated / mixed]
- Domain age: [e.g., 3 years]
- Current open rate by provider: [e.g., Gmail 22%, Microsoft 18%, Yahoo 25%]
- Current bounce rate: [e.g., 0.8%]
- Current complaint rate: [e.g., 0.05%]
- Recent changes: [e.g., migrated ESPs last month, added new IP, none]
This skill captures the SendPost Way — a diagnostic methodology built from managing IP pools processing 10-18 million messages daily and consulting for ESPs handling billions of emails. The approach is systematic, data-driven, and built on a core belief: 95-99% of deliverability problems can be solved through four pillars at the ESP/send-engine level.
How to Use This Skill
Two modes. Pick based on what the person is asking for:
Audit mode — they want a proactive review ("audit my email setup", "we're launching, what do we need to get right?", "check my deliverability"). Run the Audit Checklist below, report findings by severity, and end with a prioritized fix list.
Diagnose & fix mode — something is actively broken ("emails going to spam", "open rates dropped", "we got blocklisted"). Follow the SendPost Way in order:
- Triage — Classify the problem type (see Triage section)
- Diagnose — Walk through the Four Pillars framework
- Recommend — Provide a specific fix plan with timeline
- Monitor — Define what to watch during recovery
Either way: be direct, be honest about what's broken, and focus on root causes rather than symptoms. If the data shows something is bad, say so clearly. And keep the language plain. "Your SPF record has too many DNS lookups" beats "You've exceeded the RFC 7208 specification limit for mechanism evaluations."
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.
- 11d ago First seen · 363 lines · 189 tokens per session scan A 4e3fe40629c2
email-deliverability is a skill published in the GitHub repository sendx/email-skills (8 stars, last pushed 1mo ago), licensed MIT. It adds 189 tokens to every session and 5,176 once invoked, about $0.0009 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 2026-08-31.
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