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 randommonicle/claude-skills --skill email-delivery-verificationgit clone --depth 1 https://github.com/randommonicle/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/randommonicle/claude-skills/email-delivery-verification)<a href="https://agentmods.dev/skills/randommonicle/claude-skills/email-delivery-verification"><img src="https://agentmods.dev/badge/skills/randommonicle/claude-skills/email-delivery-verification/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/randommonicle/claude-skills/email-delivery-verification"><img src="https://agentmods.dev/badge/skills/randommonicle/claude-skills/email-delivery-verification.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 | $0.00120 | $0.00603 |
| Opus 5 | $0.00060 | $0.00302 |
| Sonnet 5 | $0.00024 | $0.00121 |
| Haiku 4.5 | $0.00012 | $0.00060 |
Grade A, and why
email-delivery-verification 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 — 44 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Email delivery verification
Three occurrences across two repos, all the same shape: the API returned success, the team believed the mail sent, and it silently never arrived. A corporate filter hard-blocked the whole message over an attachment type; a wrong operator address hard-bounced once and the provider's account-level suppression list swallowed every subsequent send to it, forever and silently.
The rules
- 2xx means queued. Actual delivery status (delivered / bounced / suppressed) lives in the provider's dashboard or webhooks — read it there when a send matters, and after any recipient change.
- Check the suppression list as part of any "never arrived" diagnosis. One hard bounce can suppress an address account-wide; subsequent sends return 2xx and go nowhere.
- Verify every recipient leg. Multi-recipient flows fail per-leg: the customer email worked while every operator notification was suppressed. Checking one leg proves one leg.
- Confirm a mailbox exists before addressing it — the suppression cascade starts with one send to a mistyped or unprovisioned address.
- Corporate filters block whole attachment classes.
.htmlattachments get the entire message rejected by M365/Mimecast-class filters: deliver links, attach only tolerated formats (a DOCX passes where an HTML file does not). For recipients on a firm's own domain, a recipient-side block can only be fixed by their IT allowlisting the sender. - A sandbox sender reaches only verified addresses — verify the sending domain before relying on any send in the field.
What this skill does not do
It does not choose failure semantics for the send-then-record path (outbound-side-effect-idempotency) and does not govern email content. It is the delivery leg of verify-the-effect, split out because the mechanics are provider-specific.
Why
Email is the one side effect whose failure mode is designed to be silent: providers accept first and fail privately. Every incident in the evidence was discovered by a human noticing absence, days later. Evidence: ICC LESSONS_LEARNED L-004, L-015; ASH CLAUDE.md DNS/Email lesson (2026-05-21).
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 · 44 lines · 120 tokens per session scan A bde77323d199
email-delivery-verification is a skill published in the GitHub repository randommonicle/claude-skills (23 stars, last pushed 5d ago), licensed Apache-2.0. It adds 120 tokens to every session and 603 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 2026-08-31.
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