Your email subject lines determine whether your campaign gets opened or ignored. No matter how strong your email copy is, it counts for nothing if the subject line fails to earn a click.
Why Subject Lines Are So Difficult to Perfect
The ideal email subject line is attention-grabbing, clear, and relevant — but what works varies significantly by audience. As Mailchimp puts it: “The best email subject lines are short, descriptive and provide the reader with a reason to explore your message further.” There is no universal formula, but there are ground rules that consistently improve performance.
Six Techniques That Improve Email Subject Lines
1. Avoid spam filter trigger words
Words such as FREE, WIN and OFFERS are among the worst spam filter offenders. Beyond filters, Mailchimp research shows that words like “Help”, “% Off” and “Reminder” reduce open rates even when they do pass the filter. Keep a reference list and check against it before sending.
2. Control your character length
Keep subject lines to a maximum of 50 characters as a general rule. Mobile devices typically display around 30. If your audience is highly targeted and specialist, a longer subject line can work — but lead with the most important information regardless.
3. Choose between personalisation and localisation
Including a recipient’s first name is good practice, but localisation has a stronger impact on open rates. Referencing a city, town, or region makes the email feel specifically relevant to that reader. Where possible, use both.
4. Be clear about what is inside
Clever or playful subject lines can work, but never mislead the reader. If a recipient opens an email and finds something different from what the subject line implied, they will unsubscribe. Offer genuine value and make it obvious.
5. Lead with your strongest point
Readers skim subject lines in a fraction of a second. Put your most compelling element at the start so it stands out even on a crowded screen or small device. Do not bury the hook at the end.
6. Create urgency with time-sensitive language
Including a specific date or deadline makes your subject line feel fresh and relevant rather than templated. Urgency improves open rates for promotional campaigns. Just avoid using “% Off” or “SALE” in the subject line itself.
Putting Subject Lines in Context
Strong email subject lines are only one part of effective email marketing. Once you have earned the open, the copy must deliver. See our post on writing great email marketing copy for the next step, and our guide to personalising email marketing automation for longer-term performance.
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