cold-email-deliverability

cold-email-deliverability is a skill for Claude Code from cmj-hub/claude-cold-email. It costs 134 tokens per session (1,374 once invoked), scanned A, original, MIT.

A checklist for checking whether an email-sending domain is ready for a cold-email campaign. It examines DNS records such as SPF, DKIM, DMARC, MX, and BIMI, along with reputation, sending history, and message content.

In plain words
What is it for?
It is for reviewing domain authentication, blacklist and mailbox reputation, sending-volume warm-up, reply rates, and spam-related content issues, then giving a score and repair order.
Why use it?
It helps find configuration or reputation problems that can send campaign emails to spam or prevent delivery before messages are sent.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Part of the cold-email plugin — 12 skills, 2 agents shipped together

Good fit It is for reviewing domain authentication, blacklist and mailbox reputation, sending-volume warm-up, reply rates, and spam-related content issues, then giving a score and repair order.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/cmj-hub/claude-cold-email/cold-email-deliverability
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 cmj-hub/claude-cold-email --skill cold-email-deliverability
Clone the repo
git clone --depth 1 https://github.com/cmj-hub/claude-cold-email

Made for: Claude Code.

Or install cold-email, the plugin that ships this one along with the rest of its 12 skills, 2 agents.

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.

agentmods badge for cold-email-deliverability

README.md
[![agentmods](https://agentmods.dev/badge/skills/cmj-hub/claude-cold-email/cold-email-deliverability/github.svg)](https://agentmods.dev/skills/cmj-hub/claude-cold-email/cold-email-deliverability)
Your own site
<a href="https://agentmods.dev/skills/cmj-hub/claude-cold-email/cold-email-deliverability"><img src="https://agentmods.dev/badge/skills/cmj-hub/claude-cold-email/cold-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.

agentmods 80×15 button for cold-email-deliverability

Your own site · 80×15
<a href="https://agentmods.dev/skills/cmj-hub/claude-cold-email/cold-email-deliverability"><img src="https://agentmods.dev/badge/skills/cmj-hub/claude-cold-email/cold-email-deliverability.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 134 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,374 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00134 $0.01374
Opus 5 $0.00067 $0.00687
Sonnet 5 $0.00027 $0.00275
Haiku 4.5 $0.00013 $0.00137

Measured 2d ago against content hash a8588abf22dd, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

cold-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 2d 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/cold-email-deliverability/SKILL.md · 138 lines

How it starts

The opening of the file, as written. The whole thing — 138 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Cold Email Deliverability — 15-point pre-campaign domain health

Loaded by cold-email when the user asks about deliverability, SPF/DKIM/DMARC, domain health, or "are we ready to send."

Activation triggers

  • "Check deliverability"
  • "Domain health"
  • "SPF / DKIM / DMARC"
  • "Are we ready to send"
  • "Pre-campaign check"
  • "Why are we landing in spam"
  • "Inbox placement"

Workflow

1. Inputs

Ask for:

  • sending_domain — e.g. outreach.jmc.com
  • from_address — full address used in the From: header
  • inbox_provider — GSuite / O365 / Smartlead / Instantly / custom
  • mailbox_age_days — how long this address has been sending
  • current_daily_send_volume — emails/day
  • recent_reply_ratio — % over the last 14 days (skip if first campaign)

2. Run the 15 checks

The 15 checks span four categories:

# Category Check How
1 DNS SPF record exists dig TXT <domain> for v=spf1
2 DNS SPF includes inbox provider Lookup includes match provider
3 DNS SPF lookup count ≤10 Resolve all includes recursively
4 DNS DKIM selector resolves dig TXT <selector>._domainkey.<domain>
5 DNS DKIM key ≥1024 bits Decode the p= value
6 DNS DMARC record exists dig TXT _dmarc.<domain>
7 DNS DMARC policy ≠ none for cold outreach p=quarantine or p=reject required for bulk senders post-Feb 2024
8 DNS DMARC has rua= reporting Aggregate report URI configured
9 Reputation Domain not on Spamhaus / SURBL Lookup against public blacklist APIs
10 Reputation rDNS / PTR record matches sending IP dig -x <sending-ip> matches forward
11 Warm-up Mailbox age ≥21 days Compare mailbox_age_days to threshold
12 Warm-up Daily send ramp ≤30/day for first 14 days Compare current_daily_send_volume
13 Warm-up Reply ratio ≥3% over 14 days (Hard threshold for B2B cold)
14 Content TLS support on MX Confirm STARTTLS advertised
15 Content DKIM signs the body, not just headers Test message via test tool (mxtoolbox)

Read the full file on GitHub · 138 lines

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.

  1. 2d ago Changed · -2 lines a8588abf22dd
  2. 11d ago First seen · 140 lines · 134 tokens per session scan A efb45fb76fb6

Subscribe to this mod's changes

cold-email-deliverability is a skill published in the GitHub repository cmj-hub/claude-cold-email (2 stars, last pushed 2d ago), licensed MIT. It adds 134 tokens to every session and 1,374 once invoked, about $0.0007 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.