Subject lines are the cover art of the inbox.  Just as the cover shot determines news stand sales and readership, subject lines are often the subscriber's deciding factor to open vs. delete a message.  Unfortunately, they get too little attention from marketers.  Especially because the secret to great subject lines (and higher response) is readily available in every marketer's response data.

In my kickoff column, I outlined eight strategies for earning higher revenue from the email channel.  This month, we take a deep dive into the seventh of these: Optimizing subject lines.

Oh woe to the poor, neglected subject line. For something so important, it usually gets two minutes of rushed thought just as the message is getting set up in the system. In my informal poll of marketers at an email marketing conference in June, nearly all of the 200 professionals in the room said that they rarely discuss subject line alternates prior to mailing and only a handful do any regular testing.  That is a missed opportunity to improve response rates.

The best measure of subject line effectiveness is not open rates alone – it's click-to-open rates.  This is a more true measure of engagement.  It doesn't matter how many people open (other than the branding benefit) if they don't click or take action on the content. Even with publisher newsletters, engaged subscribers do more than merely skim headlines – we want to make it easy and compelling for them to click to learn more about a particular article or offer.  In all this, the subject lines must be closely aligned to the topics and offers, and the content has to follow up completely on the promise of the subject line. 

Sounds simple in concept, but implementation can be daunting. Like anything in marketing, however, there are no universal magic bullets like optimal length, keywords or even the best day of the week.  

Instead, let the data guide you.  I often find that there is, in fact, a set of subject line best practices for optimal opens and clicks – but that it's unique to each particular marketer.  A B2B publisher may find that longer, more descriptive subject lines and how-to content – sent on Tuesday morning -- generate the most page views and ad clicks.  But an ecommerce company may find brand names sent on Thursday afternoon earn the higher return.

You can identify the secret code for your own program.  The answer is in your data. Simply take a look at all the mailings you've done over the past quarter or year, and measure opens, clicks and click-to-open rate by factors like length of subject line, the appearance of key words, time of day and day of week. In which direction does your own history guide you? 

You may find that the subject lines that drive the highest opens do not also drive the highest sales or page views.  Do keep in mind that it may not be solely due to one factor like length - if shorter subject lines are promotions and longer are newsletters, then your engagement rates will be completely different for those different message types. Be careful to balance the evaluation. 

Once you understand the secret for your own subscribers (and note that some segments of your file may behave differently and have unique needs), then put it into practice and measure success.  For practical purposes, write the subject line at the same time the copy and call to action are written.   This will keep the synergy in step.   Always send subject lines through a content checker BEFORE you mail to be sure you haven't inadvertently triggered a spam filter.  Feel free to use words like "free" and "act now" but over-use or particular phrasing can have an impact on your sender reputation.

What I love about this approach is that it's a much better measure of actual subscriber engagement and behavior than even A/B split testing, since it can be applied across your entire program.  Take a look at your own data and start to optimize based on your own success factors.   You can also compare key competitors to see if they use the same keywords or length (and you may decide to do the opposite!).

Let me know what you think and please share any ideas or comments below.

Stephanie is a customer advocate, and an expert in creating amazing email subscriber experiences that reach the inbox, drive revenue and build brands.  Using her 20+ years of direct marketing and publishing experience, she helps online publishers and marketers optimize their email channel experience and revenue, starting with inbox deliverability. Email Stephanie at: stephanie.miller@returnpath.net