Sales email subject lines: what actually gets opened

Subject lines that get opened are short, concrete and about the recipient's world, not about your product. Two to four words in lowercase almost always beat a polished headline, because they look like an email from a colleague and not like a campaign.

Why do short subject lines work best?

Because most B2B email is opened on mobile, where the subject line is cut off after four to six words. But the more important reason is psychological: a short, unformatted subject line signals that a human wrote an email to another human. A long, capitalized headline signals a blast, and blasts get deleted in bulk.

The rules of thumb:

• Two to four words. Rarely more.
• Lowercase. "the question about the hiring" beats "The Question About The Hiring".
• No sales words. Free, offer, unique chance and percent signs belong to the spam filter.
• No clickbait. A subject line that promises more than the email delivers gets punished in the next email.

What should the subject line be about?

The recipient's world. The best raw material is the same signal that carries the opening line: a concrete event at the recipient's company. The subject line is then just a shorthand for the reason you are reaching out.

The ranking of raw material:

1. An event at their company. A hire, a new role, a launch, a move.
2. A problem in their day. Worded in their words, not yours.
3. A shared reference point. An event, a publication, a mutual contact.

What never belongs there is your product, your company name or your category. The recipient did not ask for any of it, and the subject line is the wrong place to introduce it.

What do good and bad subject lines look like?

Fictional examples, real principle:

Bad: "Streamline your sales process with the market-leading platform"

Ten words about the sender. Looks like a newsletter, treated like one.

Good: "your two sales hires"

Three words about the recipient. Raises the question of who wrote it, and that question is only answered by opening.

Bad: "Quick question"

Short, but empty. The line has been used so heavily it has become its own spam signal.

Good: "the proposal that stalled"

Concrete, slightly uncomfortable, impossible not to relate to if it hits home.

Bad: "LAST CHANCE: Book a demo before Friday"

Caps, urgency and a demo no one asked for. Three spam signals in one line.

Good: "after your switch to the new system"

References a real event and leaves the rest to the email.

Is open rate the right metric?

No, and this is the uncomfortable truth behind all subject-line advice: open rate is a broken metric. Apple's and Google's prefetching of email registers opens that never happened, and the numbers vary more with technology than with quality. An email can also be opened, skimmed and deleted in two seconds, which counts as a win in the stats but zero in the pipeline.

The metric that matters is replies. A subject line is good if the email behind it gets replies, not if it triggers a reflex open. That also means the subject line should never be written in isolation from the email: line and content should be the same thought at two lengths.

The same logic drives how Leo, Revexa's AI, works with dormant leads: the subject line is built on the signal that triggered the email, and the only thing optimized for is replies and booked meetings. Run the numbers on what your own list is worth in the calculator on the home page.

Common questions

Does the recipient's name work in the subject line?

Rarely. "Anna, a question" has been used so long that name-level personalization signals mail merge rather than care. Personalize on the event instead of the name.

Should the subject line be a question?

It can work, but the question usually does more good as the CTA at the end of the email. A statement in the subject line and a question in the email is the most common winning combination.

How many subject lines should you test?

Test by all means, but measure on replies per email sent, not on opens. A test that crowns a subject line with a high open rate and a low reply rate has picked the wrong winner.