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Usability of Email Subject Lines
by John S.
Email is very important to a lot of people and companies. However, very
little usability research has been done on email, specifically email subject
lines. This article is a summary of a research report written by WebWord on
the topic and contains several results. The basic finding from the research
is that effective email subject lines are very short,
very meaningful, and personal.
There is virtually
no research on the usability of email. That is very interesting when you
consider that in 1999 over 394 billion email messages were sent. If you also
consider that if the usability of each email was improved to yield (or save)
just $0.01, the impact would be almost four billion dollars. From
this perspective, we consider the usability of email to be very important.
There is very
little research on microcontent (headings, titles, labels, and so forth).
For the most past, the usability community has ignored microcontent. While
it is true that Jakob Nielsen wrote an article
on the topic microcontent, he provides no data to back up his various
claims. Most people have simply taken his advice at face value and no one
has followed up on his ideas.
WebWord decided to
conduct an independent usability study on email and microcontent. If an
email subject line is not effective, users will delete it. If it is deleted,
it will die and the message is lost. This is good in many cases, such as
spam, but in many other cases it is bad. Email subject lines should be of
critical importance to companies that send our email to customers. For
example, many companies send confirmation emails to customers after a
transaction on a web page. If the subject line is not very clear and useful,
there is the potential for great harm to the customer-company
Brief Overview of the Research Methodology
We tested 22 users
online using an interactive web application that we built specifically for
this research. The study had three phases. First, users were asked to look
at a wide variety of email subject lines over several trials. On each trial,
they were asked to indicate whether they would open the email, read it
later, or delete it. Second, users were presented with several groups of
emails over several trials and they were asked which email they would open
first. Finally, users were asked to rank email subject lines based on the
order they would open them. At the end of the three phases, users were asked
to answer several basic questions, relating to when and how they used email.
We also collected over 4,800 subject lines to develop a set of normative
data to share in our report. We felt that this data would do a good job
complimenting the user research.
As expected, the
data was very rich and robust. Like all of the research done at WebWord, we
found interesting answers to our basic questions. Some of the general
results are listed below:
Email subject lines should be short. Our research indicates that the shorter the subject line the better it is.
Email responses (messages prefixed by RE:) are important to people.
Forwarded email messages (prefixed by FW: and FWD:) are not as critical or important to people in relation to other
The use of ALL CAPS only marginally improves usability. It seems to be a non-factor compared to the other factors.
Position of an email in a list of other emails is not relevant.
The basic idea is
that email messages should be short. If they are personal, as referenced by
the RE: prefix, then they are more likely to be read and they are more
important to the recipient. It doesn't seem to matter when the user receives
the email and it doesn't seem to matter what emails are flanking other
emails. Our usability research verifies what usability researchers have
suspected: Keep email subject lines short and keep them personal if they are
meant to be personal.
The normative data
was very interesting. I'm not going to give the whole story away but the
basic idea is that most email subject lines (45% of the 4,800) are greater
than 50 characters in length. On the other hand, the short and effective
email subject lines only accounted for only about 15% of all the emails. So,
even though common sense might indicate that shorter email subject lines are
better, the reality is that most people don't follow the common sense idea.
This is yet another small victory for usability testing!
Caveats and Final Comments
I'm going to start
by saying that our research has limitations. For those folks that understand
human psychology and usability testing, you will see that there are a few
methodological flaws. I'm not going to discuss those problems in this space
because the results are still relevant despite the flaws. I'm keeping this
article pure as I hope you understand.
Next, I wanted to
let you know that I've only provided you with about 70-75% of the results.
Obviously I have other comments. Furthermore, I didn't really dive into the
normative data, which as you can probably imagine is quite
Finally, I wanted
to let people know that you can now download the report for free! This article gives you the main ideas and
you don't need to read the full report. However, the full report gives you
more of a background on the research. We dig into the methodological
details, the results, and the limitations. The report is what you should
read if you are interested in learning more about usability research. You
should also consider getting the full report if you want to better understand
how WebWord does research and writes reports.