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    B2B cold email subject lines

    By Joshua at SunMatch Advisors · Updated · 3 min read

    What the data says

    Belkins and Reply.io looked at 5.5 million B2B cold emails sent in 2024. A few findings are worth building on:

    • Short wins. Subject lines of two to four words had a 46% open rate. Ten-word ones had 34%.
    • Personal wins bigger. Personalized subject lines had a 46% open rate against 35% for the rest, and a 7% reply rate against 3%.
    • Questions do well. Subject lines phrased as a question matched the best open rate, 46%.
    • Urgency hurts. Words like "ASAP" pulled open rates below 36%.
    • Numbers don't matter much. Subject lines with numbers opened at 27%, without at 28%.

    One caution: some email apps load images automatically, which counts as an open, so open rates are rough. Replies are the number that matters.

    A simple formula

    Name the specific thing you're offering, and tie it to them: [what you offer] for [their company], or [what you noticed]. It should read like a note from a person, not a headline.

    Examples by situation

    • You sell a product: "Shipping cases for Riverbend"
    • You noticed something new on their site: "Cases for the variety box"
    • Something about their operation: "Boxes for 300 morning drops"
    • You're offering something free: "Free samples for Golden Hour"
    • You need the right person: "Packaging at Riverbend"
    • Follow-ups: no new subject. Reply in the same thread so it reads as one conversation.

    Example companies.

    Subject lines to avoid

    • A fake "Re:" or "Fwd:" on a first email. It's misleading, and CAN-SPAM requires honest subject lines.
    • Urgency: "Urgent", "ASAP", "Last chance". It reads as pressure from a stranger.
    • Vague openers like "Quick question" or "Following up" on a first email. They could be from anyone.
    • All caps, exclamation marks, and anything the email doesn't deliver.

    How we write them

    Every subject line we send is a few words long and comes from one real detail about the company it goes to. A check runs before anything sends and blocks words like "urgent" and any exclamation marks, and follow-ups stay in the original thread. The subject line gets the email opened; the email itself has to earn the reply. See how our cold email outreach works.