What a subject line has to do#
In a crowded inbox the subject line, the sender name and the first line of the email are read together. The subject line's job is narrow: make it clear the email is for this business and about something real. The opening line does the persuading.
That is why the best cold subject lines look almost boring. “Phone-only bookings” tells a practice owner exactly what the email is about. “Quick question” could be anything, and readers know it.
Rules that hold in every sector#
- Three to six words, so it isn't cut off on a phone
- Sentence case; no words in capitals, no exclamation marks, no emoji
- About them, not you: their detail, their area, their service
- Honest: the email must be about what the subject line says
- No fake “Re:” or “Fwd:” on a first email
- No spam-style words such as “free”, “guaranteed” or “urgent”
30 examples by type#
| Type | Examples |
|---|---|
| The observation | Phone-only bookings · Your menu is a PDF · Contact form not sending · No prices on the site · Booking button hidden on mobile · Last post from 2023 |
| Their business, plainly | Online booking for Example Dental Clinic · Reviews for your Leeds garage · Bookings at your Bath studio · Quotes for your kitchen fitting work · Booking page for your Clifton café |
| A specific outcome | Evening booking requests · Fewer no-shows · Quote requests at weekends · Repeat orders by email · Fewer missed calls |
| A short question | Bookings after 6pm? · Who handles your reviews? · Still taking new clients? · Worth a look? · Menu online by spring? |
| Context or connection | After the trade show in Birmingham · Following your post about the new site · Suggested by your web agency · Your Camden and Islington sites |
| Follow-ups (same thread) | Re: Phone-only bookings (genuine reply in the thread) · Example for your practice · Closing the loop · One last idea · Weekend booking example |
Fictional examples. Use only the ones that match what your email really says; a connection must be real.
Subject lines to avoid#
| Avoid | Why | Instead |
|---|---|---|
| Re: our call | Implies a conversation that never happened | Bookings after 6pm? |
| Quick question | Says nothing; reads like a template | Who handles your reviews? |
| FREE audit for your business! | Capitals, exclamation mark, spam wording | Your contact form isn't sending |
| Partnership opportunity | Vague and about you | Quotes for your kitchen fitting work |
| [First name], you'll love this | Over-familiar, and a merge-tag giveaway | Phone-only bookings |
The preview line counts too#
Most mail apps show the first words of the email next to or under the subject. If your first line is “Hope you're well” or “My name is…”, that is what the reader sees. Start with the observation instead, and the subject and preview work as one sentence.
How to test subject lines with small lists#
With a few hundred emails a month, an A/B test of subject lines rarely produces a clear winner, because the difference is lost in noise. Change one thing at a time, compare reply rates over several weeks and keep notes.
Don't use open rates to decide. Apple Mail Privacy Protection downloads remote content in the background, so emails can be counted as opened whether or not anyone read them. Replies and meetings are the numbers that count.
How Repmight helps#
Repmight writes the subject line from the observation it found on the business's website, so it is specific by default. It then tracks which subject lines and observation types get replies in your own campaigns and uses the best ones as examples for new drafts.
FAQ
What is a good subject line for a cold email?
Three to six plain words about the recipient's business, usually the detail you noticed, such as “Phone-only bookings”. It should describe what the email is about.
Should a cold email subject line be in lowercase?
Sentence case is safest: a capital at the start and nowhere else. All lowercase can look careless; capitalising every word looks like a newsletter.
Is it OK to use “Re:” in a cold email subject line?
No. On a first email it pretends a conversation already happened, which damages trust and, in the US, can count as a deceptive subject line. Use “Re:” only on genuine replies in the same thread.
Should I put the recipient's name in the subject line?
The business name can help when it is natural, such as “Online booking for Example Dental Clinic”. A first name with an exclamation mark reads like a mail merge.
How long should a B2B subject line be?
Three to six words is a good range. Longer subject lines are often cut off on phones.
Sources
- 15 U.S. Code § 7704: Other protections for users of commercial electronic mail · U.S. Government Publishing Office
- Mail Privacy Protection & Privacy · Apple
- Email sender guidelines · Google