"Free" is not a Dirty Word (and 4 other Subject Line Findings)

With so many things on an email marketer’s plate, the subject line is often an afterthought. And yet, the subject line (and the friendly from name) have the largest impact on your open and read rates. Of course, a well crafted subject line falls on deaf ears if the recipient is not the right target. However, once you have segmented your audience and are sending targeted content, a great subject line can be the difference between a campaign that drives your subscribers to read your email or simply put in the the trash (or ignore it all together). Given the impact subject lines can have on taking your targeted campaigns to the next level, we decided to use some Return Path data to review some subject line best practices.

Personalization works. Only when it doesn’t. For personalization, we looked at the use of a person’s name at the beginning of a subject line and saw that for five of the categories we reviewed, we were able to see a statistically significant difference.  For three of the categories (Hotels, Health and Beauty, and Home), the use of a person’s first name led to a higher read rates. However, for Music, Movies, and Games and Retail, the use of a subscriber’s first name actually hurt the read rates.  When determining whether the use of a person’s first name, consider the type of relationship you have with the subscriber and the type of email that is being sent. Subscribers are likely to have more personal connections with some brands or categories of senders than others. Industries (like Hotels) that are more likely to have loyalty programs can likely benefit from the use of personalization more than companies that are promoting the latest video game or music hit. Also, employing personalization beyond the use of first name is another way to take your subject lines to the next level.

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Shorter is better (most of the time). Of all the data points we looked at, the length of the subject line was the most clear cut. Of course, with all things email marketing, there are always exceptions to the rule. However, subject lines that were less than 50 characters generally had a higher read rate than subject lines that were longer than 50 characters. We also looked at subject lines that were shorter than 25 characters. Here again, the trend for most categories was that subject lines shorter than 25 characters outperformed their longer counterparts. If you don’t have time to test your subject lines, the data show that shorter is probably better when it comes to subject lines.





Symbols are Losing Their Luster.   In the three categories where we saw a statistically significant difference for subject lines using symbols, we can see that the use of symbols in the subject line hurt read rates. Of course, I’ve seen individual senders that have seen an increase in read rates when using symbols. My co-worker,  Guy Hanson, has also done some analysis with the placement of symbols within the subject lines. His findings have concluded that if you are going to use a symbol in a subject line, you’re best putting it as the first element in the subject line.  Guy has also written a blog that explores symbols a bit more in depth for some specific senders. As with all things email marketing, spammers have taken to using symbols in their subject lines. Because your program is unique, make sure to test (and closely monitor results) to determine how you can best take advantage of one of the the latest email marketing trends (and if you’re going to use a symbol without testing it, put it as the first element in your subject line!).


“Free” is not a dirty word. Even though IP reputation (and now domain reputation) are the main reasons emails end up in the junk/bulk folder, we are often asked if using the word “free” in a subject line is going to result in an email being marked as spam by Mailbox Providers. For most of the categories, there is only a slight variation in inbox placement rates for subject lines that contain the word “free” – some a bit higher and some a bit lower.  Only for senders in the Jewelry category did we see a marked dip in Inbox Placement Rates for subject lines that contain the word “free” in the subject line. If you’re concerned about Inbox Placement Rates, using the word “free” in your subject lines is likely not your problem. Focus on other elements of your program that are likely causing deliverability problems: frequency, relevancy, and delivering on email program expectations.


ALL CAPS. ALL OK. Using subject lines with all capital letters is also a tactic that has been used by spammers and generally avoided by many senders. However, when we look at senders that did use all capital letters in their subject lines, we see the same thing as we saw with the word “free.” It really doesn’t have a negative affect on Inbox Placement Rates.  However, as we know, there is a lot more at play with Inbox Placement Rates than the subject line. Using all capital letters in a subject line may make sense in certain situations, but with anything that is a bit “out of the norm” we recommend testing it out and only using in certain situations.  The good news is that if you have a situation where it might make sense to use all caps (e.g., you’re big annual sale), you can test out the use of all CAPS to see if it makes it to the inbox and increases your read rates.



For this analysis, we looked at subject lines for over 2,900 domains across several different categories for a 2 week period at the beginning of August.

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