Subject lines: what actually moves the open rate

A subject line has one job: to get the email opened by the people it was written for, and left alone by everyone else. It is not a headline and it is not an advertisement. It is the answer to the question a reader asks in the half second before they scroll past: is this for me, and is it worth a minute right now?

Say what is inside

The subject lines that hold up over months are the plain ones. "Three dates added to the tour" outperforms "You won't believe what's coming" every time, because the first one lets the reader decide and the second one asks for trust it has not earned. A subject line that is clear about the content also protects you later: a reader who opens expecting one thing and finds another remembers it, and opens the next one less often.

Put the important words first

On a phone, a subject line is cut off somewhere between thirty and forty characters. Whatever you put after that point is invisible to most of your readers. Lead with the thing that matters and let the rest trail off: "New album out Friday, plus tour dates" works when it is cut; "Some news from us this week about the new album" does not.

Use the sender name too

The name next to the subject is read first, and it carries more weight than most people give it. It should be a name the reader recognises: the artist, the shop, the person who writes the newsletter. A subject line does not have to repeat who you are if the sender name already says it, which frees up those first thirty characters for something useful.

The preview text is the second subject line

Most inboxes show a line of the email's content right after the subject. If you do not set it, the reader sees whatever comes first in the message, which is often "View this email in your browser". Write it on purpose, as the sentence that follows the subject: subject "Three dates added to the tour", preview "Lisbon, Porto and Madrid, tickets from Thursday".

Things that do not work as well as people think

• Capitals and exclamation marks. They read as shouting, and spam filters have seen them a billion times.
• Words like free, urgent, last chance and act now. The same reason, twice over.
• Emoji at the start of every subject. One, now and then, can help a subject stand out. In every email, it becomes wallpaper.
• The reader's first name in the subject. It felt personal in 2010. Now it mostly signals a merge field.
• A question the reader can answer with no. "Ready to upgrade?" invites exactly that answer.

Test it instead of guessing

Your readers are not everyone's readers. The only way to know which of two subject lines works for them is to send both: half the list gets version A, the other half gets version B, and the report shows which one was opened more. Run that on the campaigns that matter, keep the two versions genuinely different (a different angle, not a different comma), and after a few months you will know what your list responds to better than any guide can tell you.

MBX Reach has the subject A/B test built into the campaign editor on the plans that include it: write the second subject, send as usual, and the report names the one that got more opens.

MBX Reach is email marketing for small teams: lists, campaigns, automations and reports, in six languages.