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  • Writer's pictureTom Kothman

How to write the best email subject lines to boost open rates.

Creating an email subject line takes more than good writing skills -- it requires a deep understanding of your target customer and the ability to take a larger message and distill it into a few effective words.

The two biggest email subject line mistakes are

  • summarizing benefits, hence no curiosity or need to open or

  • demonstrating that you are irrelevant to the recipient’s interests.

The most important job of a subject line is to get your emails opened. Using curiosity, you create a question that can only be answered by opening email.

Six ways to generate curiosity in email subject lines

1. Questions

2. Unfinished stories

3. Unexpected

4. Imply you have info they don’t

5. Imply they have forgotten something


Being relevant immediately conveys that there is a reasonable chance of finding something of value.

Six ways to exhibit relevance in email subject lines

1. Start a conversation

2. Personalization

3. Problem solving

4. Prior action follow-up

5. Re-engagement

6. Key words*

*Using relevant key words in the subject line is doubly useful. Not only does a key word in a subject line instantly communicate a relevant topic and helps with SEO but putting key words into the email makes it searchable within the recipient’s email box or folder. Did you ever try finding an email on topic X that piqued your interest but is now buried under 183 emails received since then? The right keyword provides the proverbial buried treasure map.

Emoji in email subject lines

And then there are emoji. I cover them here because they have become a frequent and legitimate element in subject lines.

Merriam Webster defines emoji as “: any of various small images, symbols, or icons used in text fields in electronic communication (as in text messages, email, and social media) to express the emotional attitude of the writer, convey information succinctly, communicate a message playfully without using words, etc.”

In other words emoji set a tone. According to KEAP

“Think of emojis [sic] like salt in a dish, add just a little and it elevates everything, but too much and your guests will be running for the exits.

The top 3 emojis [sic] for increased open rates:



As it turns out, emoji placement also affects recipients’ perception of a subject line.

Shelley Walsch, founder of content marketing agency ShellShock, tested 3.9 million emails. She found that 7 out of 12 analyzed campaigns indicated that including an emoji at the end of a subject line resulted in a better open rate than when the emoji is at the beginning.”

According to Experian, 56% of brands using emojis in subject lines. Several ESPs such as ActiveCampaign have added Emoji libraries to their email editors, eliminating the need to search for emoji on third party emoji libraries like

Writing Email Subject Lines that Boost Your Open Rate

The goal of the email subject line is to get your subscriber to open your email. Here are some tips to keep in mind:

  • Keep the subject line short – 7 words and 41 characters are optimal.

  • Use emojis to help your subject line stand out. Just don’t overdo it.

  • Make the subject line unique to the recipient. Be personable but professional.

  • Take the time to A/B test your subject lines. Compare open rates and analyze the ‘why’ behind it.

  • Find the balance between trendy and personalized.

  • Craft a subject line you would open!

Caution: Open Rates are still important but are less valid as a performance indicator in 2022.

As Apple’s MPP and other efforts have inflated email open rates and made this traditional KPI less useful, email marketers are focusing more on other performance measurement KPI’s.

“Previously, when a recipient opened an email using Apple Mail, Apple cached the image at the moment the reader opened the email—the tracked pixels were an indicator that it was opened. With this new update, the image is cached on an Apple server after an email is sent but prior to the message being viewed by its recipient, eliminating marketers’ ability to know for sure whether or not an email was opened at all. In effect, opens are no longer a useful metric to measure and design email programs and cannot be relied on as a behavioral indicator. Instead, marketers need to evolve their scorecards to shift to more substantive downstream funnel metrics such as clicks, conversion events, revenue and opt-outs.”

Quoted in Adweek

Advancing this guidance, a Marketo study found subject lines containing four words received the highest average open rates (18.26%). However, the click-to-open rate likely is more important because it encompasses both opening and clicking on at least one link – conversions. The highest average CTO rate (10.8%) happened with seven-word subject lines, closely followed by nine words (10.6%) and six words (10.1%).

The following chart comes from The Content Marketing Institute.

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