Why & How to Test Subject Lines on Your Next Email Campaign

If you took a poll of B2B marketers (see below), my guess would be that only a small percentage test email subject lines with any regularity. The usual excuses given are 1) time and 2) risk – first, that testing subject lines adds one more step to the development of a campaign that’s already behind schedule, and secondly, that testing message to half the list runs the risk of lowering overall response.

email subject line testOf course, the long-term benefits of testing subject lines far outweigh the risks. Yes, it’s one more step in the campaign process, but if you make testing a standard part of the routine, the extra time to develop test copy and set up the appropriate list splits is inconsequential. And yes, a single test message may not outperform the control, but the amount of risk depends on what you’re testing. Small, simple, isolated changes to your control message, especially as part of a systematic testing program deployed over time, render that risk fairly minimal.

The key benefit of a subject line test is not the lesson learned from one campaign. It’s the cumulative learning from systematic testing over time. If you’re testing correctly (see below), the difference in performance between control and test messages for any one campaign will likely be small anyway. But over time, those small differences add up. Over the course of several campaigns, learning how your particular audience responds to different structure, topics, key terms – and then applying those lessons to each successive campaign, can increase email response rates substantially.

Furthermore, NOT testing subject lines is dangerous for one simple reason – you’ll never know what impact your chosen subject line had on the campaign. Let’s say, for example, that your campaign tanks (never happens, I know.) Was it because you chose the wrong message? If you used only one subject line, you’ll never know. But if you test subject lines, you’ll at least have a stronger sense of whether message, or offer, or audience, or list quality was at fault.

So you’re convinced, right? Here then are a few key tips for how to implement an effective subject line test:

1. Don’t try to do too much. Test only modest changes so that the test results mean something. If the two subject lines are completely different, no matter what the results, you’ll have no idea why one performed better than the other. Optimally, keep the structure consistent and vary just a word or a phrase. If you test consistently, you’ll be able to cover the bases and test most things over time.

2. Decide what it is you want to learn. Would it be most useful to know which of two key benefits matters most to your audience? Or which of two topics is more of a hot button issue? Or whether people respond better to a “white paper” vs. an “ebook”? Give testing a purpose rather than simply selecting two subject lines randomly to run head-to-head.

3. To minimize risk, follow a few basic principles. Keep in mind there are no hard-and-fast rules to subject line structure that work 100% of the time. In fact, if you tested 100 subject lines with every broadcast, I’ll guarantee that at least one of the top performers would break a few “best practices” along the way. However, for most B2B marketers, testing just two subject lines is the norm because list size won’t accommodate anything much more. With that in mind, it’s generally a good idea to:

– always include the offer (White Paper, Webinar, Ebook)
– include at least one key benefit (cut costs, save time, increase revenue)
– use action-oriented language (Learn, Register, Discover, Download, Act Now)
– keep the subject line under 40 characters if possible (roughly equivalent to the amount of text most recipients will see in their preview pane or on their mobile device before opening the email)

4. You don’t HAVE to test subject lines 50/50. Sure, it makes things easier on the reporting end, but if you have a control message or structure that performs consistently, and your list size is large enough that you can afford a smaller sample size, it might make more sense (and be less risky) to introduce your test message to only 25% of the list.

How often do you test subject lines? Take our poll below.

For more tips on B2B email marketing, download our free white paper: “Top 10 B2B Email Marketing Mistakes.”

2 thoughts on “Why & How to Test Subject Lines on Your Next Email Campaign

  1. FMJohnson

    Hi — I appreciate this good advice. I wanted to ask, though, how it’s possible to keep a subject line under 40 characters if it’s to include the offer, a key benefit, and an action-oriented verb.

    Here are some examples created from your parenthetical suggestions:

    Webinar: register to increase revenue [37]
    Download this white paper to cut costs [38]
    Discover time-saving tips in this ebook [39]

    They sound good, but they don’t seem to say much and aren’t all that compelling. They aren’t specific enough to a particular problem or issue or audience to have much appeal. However, they’re right at the recommended character limit, so to add anything would require cutting one or more of the three essentials (offer, benefit, action word).

    How do you create a <40-character subject line with those three essentials and still include language that appeals to or resonates with the specific audience or market you're trying to reach?

  2. Howard Sewell Post author


    Thanks for the comment – good feedback. You’re definitely correct that 40 characters is a challenge that will test any copywriter, but the reality is that any verbiage beyond that limit is likely to be invisible, and so at our firm we try to work within those limits as best we can – at least so if the subject line ends up being longer, the first 40 characters deliver a compelling reason to open and read the email.

    Here are some examples of what I’d consider effective subject lines that fall under, or close to, the 40-character limit:

    Webinar: Increase Revenue by up to 400% (39)
    Report: Slash time to market for mobile apps (44)
    Ebook: 35 time-saving money mgmt. tips (39)

    Note that I don’t always use a call to action verb (“download”, “register”) if there’s already another action verb (“increase”, “slash”) in place. In the third example, there is no verb but the topic of the ebook communicates immediate, tangible value.

    Hope that helps!



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