Many marketers spend hours constructing great email layout and copy, but then treat the subject line as an afterthought. A detailed survey of over 2.2 billion emails, published this year, has revealed the most (and least) effective keywords and phrases in email marketing subject lines.

What Makes A Good Subject Line?

Much like the broader web, email is now all about usability. The subject line is one of the main things within a marketer’s control to influence customer behaviour. Having an ineffective, confusing or ambiguous subject line delivers a poor user experience for their online journey. Conversely, a subject line that is strong, effective and usable drives short and long term response rates.

Don’t Get Lost In The Shuffle

More emails are being sent out than ever before. As many as 144 billion per day, according to a Mashable report last year. With all these digital messages landing in inboxes, subject lines have to be attention-grabbing, in order to avoid emails being summarily deleted without opening.

Overall Results

Words like ‘Exclusive’, ‘Offer’ and ‘Save’ had a high open rate, but a low click rate and a high rate of unsubscribes. ‘Free delivery’ achieved 50.7% open rate variance on average, but also 82.4% unsubscription rate variance.

Terms relating to timing or recency largely did well. ‘New’, ‘Alert’ and ‘Latest’ were good performers. ‘Monthly’ was a bad performer, with low clicks and high unsubscription rates, but ‘Weekly’ was an excellent performer, with high opens and low unsubscription.

Of the keywords relating to content, ‘Video’ was by far the best performer. Traditional terms like ‘Newsletter and ‘Report’ were poor. But the oh-so-modern ‘Webinar’ performed even worse.

Retail & Ecommerce

Forget ‘Cheap’ and forget ‘Free’. Both of these saw dire open and click-through rates. ‘Birthday’, ‘Christmas’ and ‘Holiday’ did badly too,with the latter returning an 88.2% unsubscribe rate compared to industry average. ‘Sale’ fared better on clicks and opens, while ‘Free delivery’ was one of the better performing titles in the generally depressing retail and ecommerce category.

B2B Publishing

For B2B publications, ‘Review’, ‘Update’ and ‘Special’ all test well, indicating an interest in added value and expert insight. Open rates on contest and competition emails were low, but clicks were higher than average, even for ’spammy’ words such as ‘Win’. ‘Newsletter’ did better in the B2B sphere, with ‘Video’ and ‘Limited’ also getting higher clicks and opens.

B2B Events

Trying to get professionals to attend a trade event? Not all keywords are created equal. Many of the ‘incentive’ terms, like ‘Early bird’, ‘Last chance’ and ‘Offer’ did badly. ‘Exclusive’, ‘Invitation’ and even ‘Download’ performed well across the board, with high opens and low unsubscribes.