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 rampstackco/claude-skills --skill email-deliverabilitygit clone --depth 1 https://github.com/rampstackco/claude-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/rampstackco/claude-skills/email-deliverability)<a href="https://agentmods.dev/skills/rampstackco/claude-skills/email-deliverability"><img src="https://agentmods.dev/badge/skills/rampstackco/claude-skills/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/rampstackco/claude-skills/email-deliverability"><img src="https://agentmods.dev/badge/skills/rampstackco/claude-skills/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 | $0.00110 | $0.02695 |
| Opus 5 | $0.00055 | $0.01347 |
| Sonnet 5 | $0.00022 | $0.00539 |
| Haiku 4.5 | $0.00011 | $0.00269 |
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.
How it starts
The opening of the file, as written. The whole thing — 284 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Email Deliverability
Get email into inboxes, not spam folders. Set up authentication. Monitor reputation. Diagnose problems before they hurt the business.
When to use
- Setting up email for a new domain
- A meaningful percentage of email is going to spam
- Customers report they're not receiving emails
- Setting up DMARC, SPF, or DKIM
- Hardening against domain spoofing
- Migrating email service providers
- Sender reputation has dropped
- Pre-launch audit before sending volume increases
When NOT to use
- Writing the email content itself (use
email-sequences) - Designing the email program strategy (use
email-sequences) - DNS records in general (use
domain-strategy) - Outbound spam coming FROM your account (different problem; investigate compromised credentials)
Required inputs
- The sending domain(s)
- The email service provider (ESP, transactional service, mail server)
- Current DNS records (or access to them)
- Email volume (transactional vs marketing, daily volume)
- Current deliverability state (if known: bounce rate, spam complaints)
The framework: 3 pillars
Email deliverability rests on three pillars. Weakness in any one limits the others.
Pillar 1: Authentication
Mailbox providers verify email is actually from who it claims to be from. Three records.
SPF (Sender Policy Framework)
Lists which servers are authorized to send mail for the domain. Published as a TXT record at the apex.
v=spf1 include:_spf.mailprovider.com -all
include:adds another sender's authorized list-all(hard fail): mail from unlisted senders fails authentication~all(soft fail): unlisted senders are suspicious but pass; useful during rollout+all: never use; allows anyone to send
Only one SPF record per domain. Multiple SPF records break SPF entirely. Combine senders into a single record.
SPF has a 10-DNS-lookup limit. Each include: may use multiple lookups. Hit the limit and SPF stops working. Watch this carefully.
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.
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 · 284 lines · 110 tokens per session scan A d321d0661dbb
email-deliverability is a skill published in the GitHub repository rampstackco/claude-skills (830 stars, last pushed yesterday), licensed MIT. It adds 110 tokens to every session and 2,695 once invoked, about $0.0006 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 2026-08-30.
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