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Subject Lines
The Art and Science of Effective
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Introduction
In a world where every inbox suffers from email overload and every brand is fighting for
subscribers’ precious time, we know that most people spend just a fraction of a second
deciding whether to open, ignore, or delete a given message. A well-craed subject line can
grab readers’ aention and entice them to engage with your message rather than moving on.
For this very reason, you’ll find countless articles and reports providing tips, tricks, and
formulas for creating effective subject lines. This is not one of those reports.
The truth is, there’s no magic subject line formula that will work for every business and
every email. Using specific keywords in a particular format won’t guarantee opens. Instead,
it’s critical to test the effectiveness of various keywords and techniques to see what works
with your unique audience—and then continually optimize your email subject lines to
account for changing audience preferences.
In this report, we’ll explore why it’s important to get your subject lines right, including:
In addition, we’ll provide some data-based analysis of subject line length and keyword
effectiveness using our subject line testing solution. Although your results will vary, this
data can be used as a jumping-off point for your own campaign testing. Oh—and we’ll
also share some testing tips to help you get started.
Their impact on
conversion rates
1
How they
influence brand
perception
2
The insights that
can enhance your
overall marketing
efforts
3
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News Flash! Good Subject Lines Drive Conversions
Hopefully this isn’t really news. Perhaps the most widely accepted benefit of a strong subject line
is the ability to influence conversion rates. The reason is fairly obvious—no maer how compelling
your copy or how brilliant your design, it won’t be seen unless the subject line entices subscribers
to engage.
But a good subject line can actually do more than just affect the instantaneous decision to open,
ignore, or delete.
Continued visibility
Bank statements, receipts, personal correspondence, promotions—everything flows
into our inboxes. In a recent study by Pew Research Center, email was listed as the most
widely used smartphone feature. With the amount of time people spend looking at their
mailboxes, having your content in the inbox leaves an impression.
And unlike a fleeting Facebook ad, TV commercial, or billboard, your email will remain
in the inbox—visible to your subscriber—until they take action. Subject lines that aren’t
initially engaged with function like display ads. Their continued presence in the inbox
grants visibility and provides a reminder of your brand—and your offer. A strong subject
line increases the probability that subscribers will act on your message, either now or later.
Influence on offline purchases
Subject lines have the power to drive conversions even when your subscriber steps away
from their inbox. A clear, compelling, and memorable offer in the subject line is likely to
stick with the reader and may be recalled later in the “physical world,” leading to a point-of-
sale purchase—whether or not the original email was opened!
Of course these conversions are much more difficult to track and aribute to your email
campaign, but they definitely highlight the importance of making sure your emails land in
the inbox.
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Upscale or bargain hunter?
You invest a great deal of valuable time and resources to create campaigns that showcase
the quality and value of your company and your products. Make sure that message is
clearly reflected in your subject lines to appeal to your target audience.
For example, this subject line from luxury department store Barney’s reinforces their luxury
brand appeal by showcasing a luxury brand they carry (Givenchy) and doesn’t focus on
discounts which may not appeal or maer to their target audience.
By contrast, discount luxury goods retailer Bluefly appeals to the aspirational consumer
looking for discounts on luxury apparel. This subject line example takes a similar approach
by using luxury apparel names in their subject line, but pairs it with a discount to appeal to
their cost-conscious audience.
Know Your Audience: Subject Lines and Brand Perception
Everything your company produces contributes to your brand, whether it is a new product, a
revolutionary study, an impressive announcement, or an email subject line. Every aspect of your
company is used by customers and prospects to determine the value and quality of your brand and
compare it against your competitors.
Naturally you have an approval process to ensure that press releases and other “important”
communications are on-brand, but are you applying those same standards to your subject lines?
Emails—and the subject lines aached to them—are highly visible to your customers and potential
customers. Whether they open and engage or simply skim past, the subject line conveys a message
not only about the email content but about your brand.
Givenchy Handbags: Shop the Antigona and More Now
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Too Many Shoes? Never! EXTRA 30% Off Gucci, Prada, Jimmy Choo & More!
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Know Your Audience: Subject Lines and Brand Perception Know Your Audience: Subject Lines and Brand Perception
Make ‘em laugh
Humor can be an effective tool to make everything from speeches to advertisements and
subject lines more memorable, but they can easily backfire if humor isn’t a part of your
brand identity. Take these two examples of brands that use humor effectively based on
their audience.
Moosejaw, an outdoor apparel company, uses humor as a key part of its branding to
stand out in a competitive field, and more importantly to be remembered. This example
promoting their Easter sale is typical of Moosejaw’s absurdist style.
ThinkGeek is one brand that has humor embedded in their DNA, and nearly every
subject line they write reflects this. Truly a subject line that only a geek would
appreciate, this example from ThinkGeek promotes Valentine’s Day with a subject line
referencing the wedding scene from the movie The Princess Bride (“And wuv, tru wuv,
will fowow you foweva…”).
Highlight Competitive Advantages
Your subscribers are a combination of loyalists and bargain hunters. Make sure you
understand how your program stacks up against your competitors
• Evaluate how much subscriber overlap you have with your competitors.
• Understand how your campaign performance stacks up against your competitors,
including the subscribers you share.
• Compare messages to see what is working and what isn’t for the audience you
share. Do more of what’s working, and less of what’s not.
The Easter Platypus is Here - Up to 50% off one item
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ThinkGeek is wot bwings us togeder tooday.
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Your email results tell a story that goes way beyond campaign-specific results—if you’re willing to
do the work of interpreting them. By looking beyond the obvious metrics like opens and clicks,
you’ll find a wealth of insights that can help drive improvements across your marketing program.
Actionable insights
All of your email metrics (like read rate, deleted unread rate, and spam complaint rate)
tell you something about how your email is being perceived by your subscribers and
customers. By tracking these metrics, you can make data-backed changes to your subject
lines to increase desirable actions and decrease undesirable actions by your subscribers.
More control
Your email program, and the content you send, is wholly owned by your company. You can
quickly alter your subject lines in response to any new insights on how your campaign is
performing. You should take advantage of the control you have to not only improve your
email program, but as a testing ground for your other marketing platforms.
What are Your Emails Trying to Tell You?
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• Most subject lines were between 41 and 50 characters.
• Subject lines 61 - 70 characters long had the highest read rate (17%).
Overall, our research indicates that there is actually no correlation between the length of a subject line and its
read rate. When comparing the number of characters in a subject line to the read rate, the Pearson’s correlation*
value was -.03, which shows us that there’s no relationship between the number of characters in a subject line
and whether or not the email is opened.
Just because there’s no specific correlation between
length and read rate doesn’t mean you can fully
ignore how many characters are in your subject line.
Different devices have different display capabilities,
so it’s important to keep this in mind as you write
your subject lines.
A typical desktop inbox displays about 60 characters
of an email’s subject line, while mobile devices show
just 25-30 characters. If your audience is primarily
reading your emails on smartphones, place the offer
or call to action at the beginning of the subject line
where it’s more likely to be seen.
Being mindful, too, of how your subject lines may
be truncated can also avoid embarrassing brand
mistakes, like “license” being truncated to “lice.”
Shorter subject lines may see higher performance
for a mostly mobile audience, too. Look at your
existing data for insights like this, or use subject line
length as one of your next elements to test.
The Great Debate: Subject Line Length
The optimal length for email subject lines has been hotly debated over the years, with wildly
conflicting conclusions. We looked at emails received by over 2 million email subscribers from over
3,000 retail senders in February 2015, and found that:
Messages
Characters with this
in subject Average subject line
line read rate length
0-10 14% 1%
11-20 13% 5%
21-30 11% 18%
31-40 14% 19%
41-50 12% 25%
51-60 14% 17%
61-70 17% 6%
71-80 14% 3%
81-90 14% 2%
91-100 15% 1%
>100 9% 3%
*The Pearson’s correlation is the most common measure to determine if two sets of data have a relationship. The
values for a Pearson correlation can range from -1 to 1, with 0 showing no correlation, a -1 showing a negative
correlation, and a +1 showing a positive correlation.
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Clickbait
You won’t believe this shocking secret of geing
your emails opened: clickbait subject lines didn’t
perform that well! “Secret(s) of”-type subject lines
performed well below average (-8.69%), while “get
rid of” (+0.83%) and “what you need to know” (+0.62)
performed the best.
Benefit
When it comes to displaying benefits in a subject
line, people prefer things fast and prey—and if it’s
the “fastest” (+5.30) and “preiest” (+2.87%), you’re
more likely to get your email opened.
Keyword Effectiveness in 10 Common Subject Line Types
Marketers are a creative group, and it’s natural that they would want to write original, clever
subject lines rather than following established formulas. However, when writing subject lines and
copy, your job is to convince the reader to open your email and purchase your product, or perform
some other specific action. And while there’s always room for creativity, email subject lines tend to
fall into a limited number of predictable categories.
We looked at some of the most common keywords used in 10 basic types of subject lines, to see how
they influenced performance.
The selected keywords aren’t intended to be comprehensive, but represent some of the most
common keywords used in the emails we studied. Performance is reported in relation to other
types of subject lines sent from the same brands.
Overall, “Urgency” subject lines performed the best, followed by “Benefit” and “Command” subject
lines. Keywords commonly found in “Clickbait” headlines hope to take advantage of the curiosity
factor—and while these may work on social networks and news sites, they are far less successful in
email subject lines.
best 13.84% -0.41%
cheapest 25.14% -2.94%
easiest 19.38% +0.30%
fastest 13.59% +5.30%
preiest 32.50% +2.87%
quickest 11.09% -2.01%
Top Keywords
in “Benefit”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
get rid of 4.96% +0.83%
secret of 5.68% -8.69%
shocking 9.98% -1.22%
what you need
to know 11.06% +0.62%
won’t believe 12.90% -0.34%
Top Keywords
in “Clickbait”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
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How-To
Headlines educating readers on how to do
something may perform well for publishers, but
they don’t push results in either direction (-0.03%)
for email subject lines.
News
News-type subject lines typically convey
announcements about your products or
promotions, but keywords used in these types of
subject lines weren’t very successful at geing
subscribers to open.
announcing 15.10% -1.45%
discover 15.09% -0.09%
find 15.16% +0.58%
introducing 20.23% -1.22%
learn 12.63% -0.49%
new 14.67% +0.82%
read 14.48% -1.41%
see 12.61% -2.01%
Top Keywords in
“News” Subject
Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
Discount
Maybe it was a result of Christmas shopping
fatigue, but discount-type subject lines performed
poorly in our study. Only the keyword “offer”
prompted an upli in email read rate (+0.60%).
Command
Command subject lines generate action by telling
subscribers what to do. Subject lines with the
command keyword of “register” generated read
rates nearly 7% higher than the average. Telling
subscribers to “open” (+1.73%) and “add” (+1.13%)
was also successful.
Keyword Effectiveness in 10 Common Subject Line Types
add 16.56% +1.13%
aim 15.05% -0.86%
buy 13.56% -1.25%
call 13.47% -0.41%
click 12.27% +0.20%
download 25.03% +0.3%
get 14.92% -0.87%
open 16.48% +1.73%
put 11.49% -1.50%
register 24.19% +6.70%
try 13.71% +0.28%
Top Keywords
in “Command”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
2 for 1 6.67% -6.62%
clearance 15.06% -3.78%
discount 15.90% -0.10%
half off 10.36% -0.92%
offer 19.14% +0.60%
sale 17.77% -0.06%
save 16.16% -0.63%
Top Keywords
in “Discount”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
how to 11.97% -0.03%
Top Keywords
in “How-To”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
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Urgency
Subject lines that convey a sense of urgency were
the top performers among everything we studied.
Consider reminding people that there’s “still time”
(+15.54%) to take advantage of an offer, as opposed
to telling them it’s been “extended.” (-2.95%).
here’s how 12.47% -1.00%
steps 11.94% +1.23%
ways 13.65% +0.17%
why 12.11% -0.83%
Top Keywords in
“Reason Why”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
Price
Subject lines containing a discount with a percent
(%) or dollar ($) discount (or offering something free)
were below-average performers. It’s hard to imagine
eliminating these from your subject lines—and it’s
likely that the size of the discount or value of the free
item influences opens more than the fact that the
subject line includes a discount or offer.
Personal
Using pronouns to suggest a more personal touch
isn’t a very effective subject line strategy, only the use
of “you” yielded a (very) slight li in reads (+0.10%).
he 13.07% -0.05%
I 13.02% -0.12%
it 13.62% -0.48%
me 13.77% -0.20%
mine 8.01% -1.69%
our 15.29% -0.26%
you 16.73% +0.10%
Top Keywords
in “Personal”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
% 16.71% -1.03%
$ 15.61% -0.81%
free 16.44% -0.26%
Top Keywords in
“Price” Subject
Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
expire 19.69% -0.24%
expiring 16.60% +1.63%
extended 9.20% -2.95%
hurry 19.01% -0.47%
last chance 16.71% +1.05%
limited time 14.93% +3.05%
now 15.75% +0.24%
running out 9.92% -3.30%
still time 33.73% +15.54%
Top Keywords
in “Urgency”
Subject Lines
Average Read
Rate for Subject
Lines Containing
this Keyword
Keyword
Influence on
Read Rate
Keyword Effectiveness in 10 Common Subject Line Types
Reason Why
Reason-why headlines are a favorite with publishers,
thanks to their ability to draw in readers. (Just look at
the front cover of Cosmo next time you’re standing
in the grocery line.) Using them in subject lines can
have much the same effect. Our data suggests that
you should test subject lines that include “steps.”
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Now Start Testing!
Hopefully the concepts and data presented in this report have sparked plenty of ideas about how
to improve your email subject lines. But as we pointed out in the introduction, there’s no magic
formula—you’re going to have to do some testing to see what works for your brand and your
unique audience.
Here are some tips to help you figure out what (and how) to test.
Determine your sample
To ensure your test is valid and valuable, make sure you’re using a large enough sample
size of your subscriber base. You can either use the standard formula for sample size or
check out an online calculator like this one from Survey Monkey.
Pick your variable
The most effective tests focus on just one variable. Changing multiple things at once
makes it impossible to accurately judge which one moved the needle. When performing a
split test, make sure you are comparing apples to apples. Below are some ideas to try out
for your next split test.
• Change one or two words (examples from Victoria’s Secret)
The free tote that’s beach ready
The complimentary tote that’s beach ready
• Vary the offer (examples from Obama for America)
Upgrade: Get a free car magnet
1. Jump on Facebook 2. Get a free bumper sticker
• Rearrange the sentence (examples from Amazon)
20% off Gluten Free Snacks
Gluten Free Snacks 20% off
• Alter the length (examples from JetBlue)
Love is a trip
Flying solo? Or with a seatmate? #loveisintheair
Don’t spend too much time thinking about what to test—the keywords in this report are a
great place to start. And if your first test is inconclusive, you can always do more testing.
Methodology
For this study, Return Path analyzed over 9 million subject lines received by more than 2
million subscribers from January 1st through February 28th, 2015 using its Subject Line
Optimizer solution.
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