Which subject line words boost response rates? (+ infographic)

Five key takeaways from new email marketing research

It's the Holy Grail of subject lines, the El Dorado of email marketing...the one word that tugs magically at the heartstrings, calling siren-like to the customer to claim that click.

And it doesn't exist.

The right word(s) for a subject line depend heavily on the unique context: what you send, to whom and to what purpose.

That's why experts urge you to test for yourself. Intuition, experience and benchmark studies can only take you so far. But...subject line research does help give direction to your efforts.

Adestra just released a fascinating study which looked at over 2 billion emails to find correlations between certain keywords in subject lines and campaign response rates. The infographic is below, followed by my key takeaways.

Don't take the results at face value, of course. Context matters. But at the least, the study gives you ideas for what you might test.

Here are my five main takeaways:

1. Experiment with synonyms

When you sell an item for £10 instead of £20, you can describe this in various ways in the subject line:

• Half price
• 50% off
• 50% discount
• Save £10
• £10 off
• Only £10
• ...etc.

They all express the same concept, but they don't all "mean" the same...and they won't all trigger the same response (psychological and actual) in subscribers. Find the synonyms that resonate best with your audience. Incidentally, your pay-per-click search engine tests can provide insights here.

The Adestra survey suggests, for example, that "% off" might work better than "half price" or "save".

2. Try and impart a sense of timeliness and dynamism

In the study, words like "new", "sale", "alert" and "bulletin" were associated with higher response rates than "newsletter", for example.

This is relevant to your sign-up forms, too. You can call your list a list, newsletter, alert, bulletin, loyalty club, enews, e-specials etc. etc. Again, what does each imply? What attracts more of the right subscribers, with the right expectations?

3. Focus on benefits

Why should subject lines differ from other copy?

The highest lift to click rates reported for retailer subject lines was with "free delivery". Not something you can use, if you don't offer it. But a reminder to sell the email. Not in the sense of exaggerated claims or slogans, but in describing what it is you're actually offering the subscriber within the mail.

4. Don't underestimate the role of punctuation

How does adding or removing an exclamation mark impact subscriber perceptions? Does it emphasize the value of the statement or is it too loud? Which symbol should you use to present multiple topics:

• +
• ,
• |
• /

The survey found multiple messages separated by pipes associated with over double the positive impact on click rates when compared with commas.

5. Don't be deceptive or too clever

In the study, campaign subject lines that used "Fw:" or "Re:" had 47.5% and 42.6% lower click rates than average.

As discussed in my post on specific subject lines, a disconnect between the promise of the subject line and the actual content or offer trains people to ignore your emails.

Short-term boosts to open rates through "clever" or deceptive subject lines come at the expense of longer-term and more-important metrics, not to mention trust. You don't want to be the email that cried wolf.

Your thoughts?