Cold Email Subject Lines: 30 Formulas to Test
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Why Subject Lines Matter for Cold Email
The subject line appears alongside the sender name and, in many clients, preview text. It can help a recipient decide whether a message is relevant. These 30 formulas are writing examples, not results from a controlled campaign test.
Cold email subject lines face a higher bar than marketing emails because the recipient does not know you. There is no brand recognition, no prior relationship and no expectation. The subject line has to earn attention on its own.
What Makes a Cold Email Subject Line Work
Keep it short
Aim for a concise subject line and put the useful detail early. Display length varies by client, screen width and sender-name layout; preview the message in the clients your audience uses rather than treating 50 characters as a guaranteed cutoff.
Be specific
Vague subject lines ("Quick question" or "Touching base") are overused and signal mass outreach. Specific subject lines ("Reducing churn at [Company]") signal relevance and effort.
Avoid spam triggers
Avoid exaggerated offers and pressure language that misrepresent the message. There is no universal word list that guarantees inbox placement. Gmail’s sender guidelines require accurate subjects and sender identity alongside authentication and other sending requirements.
Personalise where possible
Use the recipient’s company, industry or a relevant event when it helps explain why you are writing. Treat personalisation as a hypothesis to test with your audience, not a guaranteed improvement in opens or replies.
Match the body
The subject line is a promise. If it says "question about your hiring process" and the email is a sales pitch, trust is broken immediately. The body should deliver on whatever the subject line implies.
30 Subject Line Formulas
Direct and specific (best for sales outreach)
- [Their company] + [your topic] -- "Acme Corp's lead response time"
- Question about [specific process] -- "Question about your onboarding flow"
- [Mutual connection] suggested I reach out -- "Sarah Chen suggested I reach out"
- Idea for [their specific challenge] -- "Idea for reducing your support backlog"
- [Their company]'s [specific metric] -- "Acme Corp's trial conversion rate"
Curiosity-driven (best for getting opens)
- Noticed something about [their company/product] -- "Noticed something on your pricing page"
- Thoughts on [relevant industry trend] -- "Thoughts on the new FTC ruling"
- [Specific observation] -- "Your checkout flow drops 40% at step 3"
- This might be relevant -- short and curiosity-provoking (use sparingly)
- Quick observation about [their site/product] -- "Quick observation about your mobile experience"
Value-first (best for establishing credibility)
- How [similar company] solved [problem] -- "How a Series B SaaS cut churn by 30%"
- [Number] ways to improve [their process] -- "3 ways to improve your email deliverability"
- [Resource] for [their role] -- "Benchmarks for VP of Marketing at B2B SaaS"
- Data on [their industry topic] -- "Data on ecommerce return rates in Q3"
- [Their company] vs industry benchmarks -- "Acme Corp vs SaaS onboarding benchmarks"
Referral and social proof (best for warm outreach)
- [Name] at [company] recommended you -- relies on a real mutual connection
- Fellow [group/community] member -- "Fellow SaaStr community member"
- We both attended [event] -- "We both attended SaaS North"
- Your talk at [event] on [topic] -- "Your talk at Web Summit on product-led growth"
- Congrats on [recent achievement] -- "Congrats on the Series A"
Question-based (best for starting a conversation)
- Is [assumption] still accurate? -- "Is your team still using Segment?"
- Who handles [function] at [company]? -- "Who handles vendor procurement at Acme?"
- Open to a quick chat about [topic]? -- keep it under 7 words
- Would [specific result] be useful? -- "Would 20% fewer support tickets be useful?"
- Have you considered [approach]? -- "Have you considered outsourcing QA?"
Follow-up subject lines (best for second and third touches)
- Re: [original subject] -- use sparingly and only for genuine follow-ups
- Following up on [topic] -- "Following up on the onboarding question"
- Any thoughts on this? -- brief and non-pushy
- One more thing about [topic] -- adds new value, not just a nudge
- Closing the loop on [topic] -- signals this is the final follow-up
What to Avoid
Clickbait
Subject lines like "You won't believe this" or "This changed everything" erode trust. If the recipient opens and feels misled, they will never open another message from you.
ALL CAPS
Writing the entire subject line in capital letters can read as shouting. Use ordinary capitalisation for clarity; capitalisation alone does not establish whether a message will be filtered.
Excessive personalisation
Using the recipient's first name in the subject line ("Sarah, quick question") has become so common in mass outreach that it now signals automation rather than genuine personalisation. Company name or specific details are more effective.
False familiarity
"Re:" or "Fwd:" on a first email is dishonest. Some recipients will open it, but the deception damages any chance of a real relationship.
Pressure language
"Urgent," "Last chance," "Don't miss out" and similar pressure tactics work in marketing to existing subscribers. In cold email to strangers, they come across as spam.
Testing Subject Lines
A/B testing
Randomly assign comparable recipients to two variants, keeping the body and sending conditions consistent. Define the outcome before sending: relevant replies, meetings or another useful action. Recorded opens are a secondary signal: Apple’s Mail Privacy Protection can load remote content in the background even when a message is not opened.
Track by segment
What works for CTOs may not work for marketing managers. Track subject line performance by recipient role, industry and company size.
Sample size matters
Choose sample size based on the baseline rate, the smallest difference you want to detect and the uncertainty you can accept. Fifty recipients per variant is not a general threshold for a reliable winner; report inconclusive results when the evidence is weak.
After They Open
A strong subject line gets the email opened. What happens next depends on the body. Keep the email short, lead with relevance to them, include a clear ask and make it easy to respond. For more on writing effective cold emails, see How to Write a Cold Email.
