Email Marketing: 4 tips for testing subject lines to help you win the inbox battle


“What’s in a name? Would a rose by any other name not smell as sweet?”
–William Shakespeare, “Romeo and Juliet”

Translation: What really matters is what something is; not necessarily what it is called.

Unfortunately for email marketers, the same concept generally does not apply when the email recipient is assessing whether or not to open your email.

For email marketers, the opposite concept is generally the rule. The email subject line along with the sender’s name in the “from” field must do all the heavy lifting for recipients to even consider opening the email and see the offer or information communicated within.


The inbox war is often won or lost by sender names and subject lines

Since the performance of your entire email campaign can often hinge on the performance of your open rate – think about it, a visitor cannot click through or convert unless they first open the email, or you can’t necessarily at least track it – it is extremely important as an email marketer to do your best in crafting effective subject lines and using sender names adding the appeal and credibility in the message required to generate an open.

Remember that you are competing against dozens, if not hundreds, of messages a day for the recipients to potentially open.

How do you determine what sort of subject lines and sender names are most effective with your list of choice? Why, through testing of course.

In this blog post, I wanted to take the time to discuss a few strategies and methods our team has used in the past to boost open rates for our Research Partners and ensure accurate results.

Before we dive into subject lines, I wanted to offer you a few tips regarding sender names. Your sender name contributes not only to the credibility of your email, but can also heighten appeal.

  • Consider how easy it is to test the sender name or if changing the sender name could have an effect on your emails’ open rate. Is this something your email platform allows you to test easily?
  • Using a corporate sender name is generally beneficial if the recipient has experience with your company or products, or if it is a well-known brand.


Tip #1. Craft subject lines around themes that you can clearly categorize and differentiate between 

Since copy is subjective and interpreted differently by each recipient, you must ensure you are testing subject lines that fall into specific themes and make sense to you and your team.

It’s also important to have a hypothesis for each subject line that explains how that subject line may influence the open rate.

You can also write multiple treatment subject lines for each category as long they accurately fall under one of your themes.

Here’s an e-commerce example for testing themed subject lines:

  • Specific incentive – “Subscribers Receive 20% off their order this weekend only”
  • Curiosity – “Don’t miss an incredible deal for subscribers, this weekend only” –  this is non-specific, given a visitor has to open to understand the “incredible deal”


Tip #2. Determine the number of subject lines you can test based on your average open rate and list size 

Since this is email testing, I recommend you test fewer than the full number of suggested subject lines in order to increase your odds of achieving results that are statistically significant and reliable.


Tip #3. Test the same treatments of subject lines in multiple sends

In my experience when testing emails with our Research Partners, I have often seen subject line performance vary widely from send to send. So if you test the same treatments in a series of email drops, you can reduce the chances of encountering a false positive in your results.

Testing your treatments in multiple sends will also help ensure that other quality assurance factors, such as timing and list splits, are consistent.


Tip #4. Dig deeper into the data during the test 

While one treatment might boost open rate, how does it affect overall clickthrough and conversion rates? Finding an answer to a tough question like this will be a little more difficult if the focus on open rate becomes an obsession.

While open rates are often used as a judge of the winning treatment, just remember there are plenty of secondary metrics that can give you much greater insight into customer behavior if you’re willing or able to take the time to look further.

Do you have any suggestions on crafting and testing email subject lines? Let me know your thoughts below.


Related Resources

Email Marketing: Promotional vs. letter-style test increases conversion 181%

Email Marketing: 6 bad habits to avoid when testing emails

Email Marketing: One question to ask yourself before you write another subject line

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