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Having studied over 3 billion emails, from over 125,000 individual email campaigns, Adestra has compiled its 2015 Subject Line Analysis Report showing what works and what doesn’t, together with ideas on how to improve results.

A subject line is one of the main things under an email marketer’s control to influence their customers’ behavior. Having an ineffective, confusing or overly-clever subject line delivers a poor user experience and can drastically affect response and even lose subscribers. Conversely, getting a subject line strategy right can make responses soar. The subject line is the key way to get your brand in front of your customers. Even if your email does not get opened, people still see your subject lines, so they deserve lots of attention.

Adestra’s research is split into four key sectors: Retail/B2C; Conferences/Events; Media/Publishing; and B2B/Professional Services/Financial.


Many sales are driven by specific percentage discounts, each of which have a substantial effect on both open and click rates. What’s interesting here is that when the discount gets larger, the open rate is less reliably improved eg ‘15% off’ only boosts click-throughs by 4%, yet cuts unsubscribes by 32%; whereas ‘50% off’ boosts click-throughs to 33%, yet only reduces unsubscribes by 13%. One potential explanation is that consumers simply don’t believe large discounts are real.


‘Agenda’, ‘Keynote’, ‘Forum’ are all key features in many events, and yet as a subject line they don’t deliver strong open rates. The reason for this is because they focus on the feature, and not the benefit. Some terms (i.e. ‘early bird’) are over-used and don’t deliver great value. But take, for example, ‘Buy’. It’s a strong call to action, often associated with retail transactions, but very effective for event invitations as well.

Massive click-through decay is largely due to a lack of creativity or propensity to experiment with other tests. The problem comes down to event workflows. Generally, the prime registration period comes in the weeks leading up to an event. The last thing marketers want to think about are subject lines! However, this is done at their own peril – considering email is one of the strongest visitor drivers out there, optimizing it is your #1 route to increased footfall.


In media and publishing different purposes are served by email, and with differing success. Strong editorial content, when used as a hero topic in the subject line, drives huge response across all metrics. For example ‘Breaking’ enjoys a +35% lift in open rates and +66% for click-throughs.

When selling subscriptions, word choice is paramount and the data shows that offers don’t work every time. It’s important to test and change things on an email-to-email basis. Careful of ‘25% off’ as that can harm open and clicks, but ‘On Sale Now’ can generate 50% better response.

B2B/Professional Services/Financial

The challenge in this sector is to stand out from the competition in an intelligent way. Bear in mind that B2B product offerings are often complex, and the sales cycle is much longer than other industries.

When unsubscribes happen in the B2B world it’s much more damaging than in B2C – especially for high-value products with a convoluted sales process. Following an email strategy that reduces unsubscribes is solid. Words such as ‘Bulletin’ (-260%) and ‘Interview’ (-98%) perform well, substantially reducing unsubscribers, but ‘iPad’ (+60%) and ‘Discount’ (+40%) are to be avoided.

For the full report, including all four sector analyses, visit