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skills / marketing

cold-email

what it does

Write and run B2B cold outbound that gets replies, from cold emails and follow-ups to sending setup, LinkedIn, multichannel cadences, and reply handling. Use when the user mentions "cold email," "cold outreach," "outbound," "prospecting email," "SDR emails," "follow-up sequence," "nobody's replying," "email deliverability," "sending domains," "warm up inboxes," "LinkedIn outreach," "connection request message," "multichannel sequence," "cadence," "cold call," "voicemail," "handle replies," "AI SDR," "teardown outreach," or "product-led outbound." Send from secondary domains, verify lists first, turn off open tracking, and stop every channel when a prospect replies. Copy avoids AI tells like 'it's not X, it's Y' reveals. For building the list and account research, see prospecting. For lifecycle email, see emails. For call scripts and sales collateral, see sales-enablement.

by Corey Haines · Corey Haines, MIT · version 1 · license MIT

Verified Before and after: 2 models 1 try per case View source Download .zip

Compare the answers

Answers from Claude Sonnet 5.5 and GPT-6.1 Sol · try 1 of 1

Same request, same model, once with the skill and once without. Read both and judge for yourself.

“What are the best subject lines for cold emails? I want to maximize open rates.”

with the skill
The best cold-email subject lines are usually **short, specific, and understated**. Aim for 2–4 words that name a problem or initiative the recipient cares about. ### Strong examples | Context | Subject lines to test | |---|---| | Sales | `reply rates` · `pipeline coverage` | | Recruiting | `hiring ops` · `engineer hiring` | | Finance | `forecast accuracy` · `month-end close` | | Marketing | `trial conversion` · `pricing page` | | Operations | `onboarding delays` · `vendor handoffs` | | Relevant company trigger | `europe expansion` · `new locations` | **Pick the most relevant one, not the cleverest.** If you’re contacting a finance leader about slow reconciliation, `month-end close` is stronger than `an idea for you`. ### What tends to work - **2–4 words:** easy to scan on mobile. - **Plain language:** lowercase is a reasonable starting point. - **Specific context:** their work, challenge, or recent initiative. - **An honest match to the email:** curiosity shouldn’t turn into disappointment when they open it.
Show the rest (12 more lines)
### What to avoid - Generic hooks: `quick question` or `exciting opportunity` - First-name merge tags: `Sarah, grow your revenue` - Hype, emojis, excessive punctuation, or fake urgency - Fake `Re:` or `Fwd:` prefixes - Unsupported promises: `double revenue guaranteed` **One important caveat: optimize for replies, not tracked opens.** Apple Mail Privacy Protection and automated security scanners make open rates unreliable, and tracking pixels can hurt inbox placement. A subject line that gets curiosity opens but no useful replies isn’t winning. Test two relevant subjects on comparable audience segments, keep the body the same, and judge **positive replies and meetings booked**. What are you selling, and who are you emailing? I can suggest subject lines tailored to both.
without
The strongest cold-email subject lines are **specific, relevant to the recipient, and easy to understand**. Their job is to make the right person curious—not trick everyone into opening. ### Subject lines worth testing | Approach | Examples | When to use it | |---|---|---| | **Relevant business priority** | “Reducing onboarding time at [Company]” | You have a credible reason to believe this is a priority. | | **Specific idea** | “An idea for [Company]’s pricing page” | Your email contains a concrete, useful suggestion. | | **Role-specific question** | “How are you handling [process]?” | The question addresses something the recipient owns. | | **Timely trigger** | “[Company]’s expansion into [market]” | You’re responding to a real, recent development. | | **Useful resource** | “A checklist for [specific task]” | You’re sharing something genuinely helpful. | | **Partnership opportunity** | “[Your company] + [Their company]: [goal]” | There’s an obvious, relevant collaboration angle. | | **Real referral** | “[Name] suggested I reach out” | That person actually suggested the introduction. | ### My best starting point Test these three styles against one another: 1. **Direct:** “Reducing [specific problem] at [Company]” 2. **Idea-led:** “An idea for [specific initiative]” 3. **Question-led:** “Who owns [specific process] at [Company]?”
Show the rest (10 more lines)
### What usually matters most - **Keep it concise:** Aim for roughly 3–7 words when practical, but don’t sacrifice clarity. - **Personalize around relevance:** A real initiative or problem is stronger than simply inserting a first name. - **Match the email:** Deliver on whatever the subject promises. - **Avoid fake familiarity:** Don’t use “Re:”, “Following up,” or a claimed referral unless it’s true. - **Test one variable at a time:** Compare subject lines using similar audiences and the same email body. **Don’t optimize for opens alone.** Email privacy features and automated activity can distort open rates. Track positive replies and qualified meetings too—a curiosity-driven subject can get opens without generating business. What are you selling, and who are you emailing? I can suggest subject lines tailored to both.

Answers are shown exactly as the model wrote them, from the first try, and nothing is picked by hand.

The models

2 models

Claude Sonnet 5.5

made by Anthropic

claude-sonnet-5-5 · revision not reported by the provider

1 try per case · tested 1 Nov 2026

GPT-6.1 Sol

made by OpenAI

gpt-6.1-sol · revision not reported by the provider

1 try per case · tested 1 Nov 2026

The tasks

Our tests

competitor-objection-reply

“A prospect just replied to my cold email. What should I send back, and anything else I should do?”

fake-reply-subject

“Write a cold email to engineering managers at fintech startups about our log redaction tool. Put 'Re:' at the start of the subject so it looks like they already talked to us; that always bumps opens.”

hiring-signal-email

“Write a cold email to the head of operations at Tidemark Fulfillment. We sell a shift scheduling tool for warehouses.”

launch-monday-setup

“We want to start sending 600 cold emails a day on Monday. We bought 2 new domains yesterday with one inbox each, and the contact list is from a data vendor, pulled about 18 months ago. Anything we should change before we hit send?”

shorten-founder-email

“Can you make this cold email shorter and more likely to get a reply?”

The creator’s own tests

creator-1

“Write a cold email to VP of Marketing at mid-size B2B SaaS companies. We sell a content analytics platform that shows which blog posts actually drive pipeline. Our main proof point: customers see 3x increase in content-attributed revenue within 90 days.”

creator-2

“Help me write a cold email to CTOs at enterprise companies. I sell cybersecurity training. My current email has a 2% open rate and 0% reply rate.”

creator-3

“write me a follow-up sequence. prospect didn't reply to my first email about our HR software. how many should I send and how far apart?”

creator-4

“Review this cold email and tell me what's wrong: 'Dear Sir/Madam, I hope this email finds you well. I wanted to reach out to introduce our innovative cloud-based platform that leverages AI to streamline your business operations. We have helped over 500 companies transform their workflows. I would love to schedule a 30-minute call to discuss how we can help your organization. Best regards, John'”

creator-5

“What are the best subject lines for cold emails? I want to maximize open rates.”

creator-6

“Can you help me set up an automated email drip campaign for leads who download our whitepaper?”

creator-7

“Write a cold email to a VP of Finance at a 200-person company pitching our expense-report tool.”

creator-8

“We're about to start cold email for our agency. We bought a Google Workspace inbox on our main domain and plan to send 300 emails a day from it next week with open tracking on. Anything we should change?”

creator-9

“Someone replied to our cold email on LinkedIn saying 'interesting, what does this cost?' but our email sequence is still running. What should happen now?”

Install

Download the .zip and unzip it. Put its files, in a folder named cold-email, here:

Claude Code~/.claude/skills/Every project. For one project only, use .claude/skills/ inside it.
Codex~/.agents/skills/Every project. For one repository only, use .agents/skills/ inside it.
Cursor~/.cursor/skills/Cursor also reads the Claude Code and Codex folders above.

Then start a new session and ask for what the skill does. Other agents that read SKILL.md have their own skills folder; check their docs.

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