Cold email subject lines, each paired with its first line

This page is for anyone writing cold emails to businesses: SDRs, founders, agency owners, recruiters. Each situation below matches a full email in the cold email templates, so you can take the subject and opener from here and the rest of the email from there. There are no open-rate promises on this page, because any honest figure depends on your list, your market and your sender reputation. Instead, the last section shows how to test your own lines without fooling yourself.

What a cold subject line has to do

Your recipient sees three things at once: your name, the subject line and the first words of the email, which most inbox apps show as a preview. They decide on all three together, in about the time it takes to scroll past.

Illustrative example. A commercial solar installer writing to the owner of a new warehouse:

The second version passes three tests:

1. Specific. It could only be about Tom's company.
2. Accurate. The email is about exactly what the subject says. That's also the law in the US: the FTC's CAN-SPAM guide says a subject line "must accurately reflect the content of the message", and Google's sender guidelines say subject lines "shouldn't be misleading".
3. Plain. It looks like something a colleague would send, not a campaign.

Subject lines by buying situation

Each card gives three subject lines, each with the opening sentence that delivers on it. Brackets are research tasks: fill them from a source you've opened, or pick a different line.

Subject: the [city] [site]
Opener: Saw that [company] opened its [site] in [city] in [month].

Subject: [site] go-live
Opener: Your [site] is due to open in [month], according to [source].

Subject: [number] sites now
Opener: With [city] open, [company] runs [number] [sites], up from [number] last year.

Subject: [area] at [company]
Opener: Congratulations on starting as [role] in [month].

Subject: the [priority] you mentioned
Opener: In your [interview or post] on [date], you said [priority] is top of the list.

Subject: [area] after the [change]
Opener: New [role]s often review [area] first, and [fact] suggests it's busy at [company].

Subject: the [role] openings
Opener: You have [number] [role] roles open, the oldest since [date].

Subject: [number] [role] hires
Opener: Hiring [number] [role]s in a quarter usually means [what it suggests].

Subject: onboarding the new [team]
Opener: With [number] [role]s joining, [process] is about to get busier.

Subject: [acquired company] integration
Opener: Congratulations on closing [acquired company] in [month].

Subject: one [process] for both teams
Opener: Your announcement said both teams will move to [system] by [date].

Subject: after the [round]
Opener: Saw the [round] news on [date]; the release says the money goes to [use of funds].

Subject: [utility]'s rate filing
Opener: [Utility] has asked regulators to raise commercial rates from [date].

Subject: [rule] from [date]
Opener: [Rule] takes effect on [date], and it covers [type of company] with [attribute].

Subject: before the [contract] renews
Opener: Your [contract] with [supplier] is due for renewal in [month], per [source].

Subject: question about [tool]
Opener: I saw in [source] that your team uses [tool] for [job].

Subject: [job] at [company]
Opener: Your [job ad or case study] says [job] is still done [how they do it].

Subject: [tool] and [the change]
Opener: Since [tool] [changed something] in [month], teams using it for [job] have had to [effect].

Subject: [referrer's first name] suggested I write
Opener: [Referrer's full name] at [company] suggested I get in touch about [topic].

Subject: introduction from [referrer]
Opener: [Referrer] said you're the person to ask about [area] and offered to introduce us.

Subject: via [community]
Opener: We're both in [community], and your post on [topic] on [date] is why I'm writing.

Subject: your question at [event]
Opener: You asked [speaker] about [topic] at [event] on [date].

Subject: your [event] talk
Opener: Your point at [event] that [point] is the clearest version of it I've heard.

Subject: the [resource] you downloaded
Opener: You downloaded our [resource] on [date], so here's the one part people ask about most.

Subject: [problem] at [type of company]
Opener: I don't have a news hook, so I'll be direct: [type of company]s like yours often [problem].

Subject: [number]-site [type] and [problem]
Opener: Groups with [number] or more [sites] usually hit [problem] around [moment].

Subject: how [peer] handled [problem]
Opener: [Customer you can name] had the same [attribute] as [company], and [what changed].

Subject: Re: [original subject] (a real reply, in the same thread)
Opener: One more thought on [the original fact]: [new detail].

Subject: [new fact] at [company]
Opener: When we spoke in [month], you said [reason]. Since then, [what changed].

Subject: closing the loop on [topic]
Opener: I won't keep filling your inbox, so this is my last note on [topic].

Three subject lines carried through a whole email

A subject line is a promise, and the whole email has to keep it, not just the first line. Illustrative examples, with fictional companies and facts.

Accounts-payable automation, hiring signal:

Subject: the three AP clerk roles

Hi Dana, you're hiring three accounts payable clerks, and the oldest posting has been up since July. When invoice volume outgrows a team, hiring is one answer; taking the keying off the team's plate is the other. We did that for a distributor with similar volume last year. Worth comparing the two before you fill all three?

Every sentence stays on the subject: the roles, why they exist, an alternative, a question about them.

Commercial solar, rate change:

Subject: Gulfline's rate filing

Hi Tom, Gulfline Power has asked the state utility commission to raise commercial rates from next July (filed 3 October). A building like yours on Commerce Drive, with 300,000 square feet of flat roof, is where solar offsets that kind of increase most directly. Would a free roof assessment be useful before the commission decides?

"Free" appears here because the assessment really is free, which matters more than the word itself (see spam trigger words below).

Corporate travel management, hiring signal:

Subject: field engineers on the road

Hi Lena, your 14 field service roles all mention up to 60% travel, across five countries. Once a team that size is on the road, the hard part usually isn't booking; it's knowing where everyone is when a flight is cancelled, and collecting receipts in five currencies. We run travel for two automation companies with similar field teams. Worth 15 minutes before the new hires start traveling?

The worked example below shows how this subject line was chosen over four others.

How long should a subject line be?

There's no reliable single number. How much of a subject line shows depends on the app, the phone, its orientation and the reader's text size, and the device tests we found disagree by several characters without fully stating how they tested. So we'd rather give you rules you can check yourself:

• Put the meaningful word first. "Greenville controls role" survives any screen; "Question about the controls engineer role in Greenville" loses its point when the end is cut off.
• Aim for two to five words. Short lines read like a note from a person.
• Use the preview. The first line fills the space after the subject, so don't spend it on "I hope you're well".
• Look before you send. Email yourself and check the inbox list on your own phone, in the apps your buyers are likely to use.

Mistakes that cost trust

Do spam trigger words matter?

Lists of "spam trigger words" (free, guarantee, act now) circulate widely, usually with no evidence attached. We can't see inside any provider's filter, and neither can the people who publish those lists. What we can read is what the providers publish, and Google's sender guidelines contain no list of words to avoid. They focus on authentication, on keeping the spam rate reported in Postmaster Tools low, and on not deceiving people: no Re: or Fwd: unless it's real, no misleading display names, no hidden content, no emoji posing as graphics.

The useful question isn't "which words are banned?" It's "would this person feel misled, or want to report this?" A plain, honest line about their business is the best protection you have. For the technical side (SPF, DKIM, DMARC and the 2024 sender rules), see the deliverability section of the cold email templates.

Write your own in four steps

1. Find the fact. The one checked thing your email is about: a new site, a hire, a filing. If you don't have one, the account research guide shows where to look.
2. Cut it to the noun. "the Kraków office" beats "I noticed you've recently opened a new office in Kraków".
3. Write the opener that pays it off. The first sentence should deliver exactly what the subject promised, with the date or source.
4. Read the pair as the inbox shows it. Your name, the subject, the first ten words. Would you open it if a colleague sent it? Does the first line make the open worth it?

Worked example: choosing a subject line

Illustrative example. The companies, people and facts are fictional, to show the method.

The seller: Tessaro Travel, a corporate travel management company. The account: Brannock Robotics (brannockrobotics.example), a maker of warehouse robots with about 600 staff. The person: the head of procurement.

The research: Brannock opened an engineering office in Kraków in September (company press release), and its careers page lists 14 field service engineer roles across five countries, each saying "up to 60% travel" (checked 20 October 2026). Finding two facts like these for every account is the slow part; Bebop researches each account and puts the trigger and the angle in its playbook, but check them before you build a subject line on them.

What makes the chosen line good: it points at the bigger, less obvious fact (a growing field team on the road most of the time, not one new office), the opener proves it with a number Lena can check on her own careers page, and it leads naturally to the problem a travel manager solves. The Kraków line isn't wasted: it becomes the new fact in follow-up 1.

How to test subject lines without fooling yourself

Opens can't tell you much. Apple says its Mail Privacy Protection "prevents senders from seeing if you've opened the email message they sent you". Open rates now mix real opens with noise, so judge subject lines by replies, and better still by positive replies.

Small tests mislead. Illustrative arithmetic. Suppose your true reply rate is 3%, and you send the identical email to two groups of 200. Each group should get about 6 replies, but chance spreads them out: an exact binomial calculation gives about a 54% chance that one group gets at least 50% more replies than the other, and about a 30% chance that one gets at least double. Now suppose a real test comes back 9 replies to 5. It looks like an 80% lift, but a standard two-proportion test gives z of about 1.1 and a p-value of about 0.28: well within what chance produces.

Here's roughly how many sends each version needs before a difference means something (two-sided test at 5% significance, 80% power, normal approximation):

Even catching a doubling from 3% to 6% takes about 1,500 sends in total. For a team sending a few dozen cold emails a day, that's weeks of volume for one test. A protocol that holds up:

1. Test one big difference. Two different angles (the hiring fact versus the expansion fact), not one word swapped.
2. Fix the sample size first. Use the table, and don't stop early because one version is ahead.
3. Randomize. Shuffle the list and alternate versions, with the same sender, body, days and times.
4. Count positive replies, plus opt-outs and complaints, per version.
5. No volume, no winner. If you can't reach the numbers, keep the version that's more specific and honest, and treat the result as a hunch.

Hypothesis: [e.g. leading with the hiring fact beats leading with the new office]
Version A subject and opener:
Version B subject and opener:
Same body, sender, days and times: yes / no
Current reply rate: ___%   Rate worth detecting: ___%
Sends needed per version (from the table): ___
How the list is split: [shuffled, alternating]
Result A: sent ___ positive replies ___ opt-outs ___
Result B: sent ___ positive replies ___ opt-outs ___
Reached the planned sends? yes / no
Decision and next test:

Self-check before you send

• The subject line could only be about this company.
• The first line delivers what the subject promised.
• The meaningful word comes in the first two or three words.
• No Re: or Fwd: unless it's a real reply, and no number you can't back up.
• Your display name is your name, not a department or a promise.
• If they asked "where did you see that?", you could answer.

Next step: take your subject line and opener to the matching full email in the cold email templates, which also covers follow-ups and the sending rules.