Have your subject line writing strategies and tactics kept up with the times? Check and see if you’re accounting for these six changes in subject line writing.

1. Subject lines need to stand on their own. 

For around two decades, subject lines and preview text have been a dynamic duo, working together to tell subscribers what an email message is about and entice them to engage with it. However, changes at major inbox providers are dramatically reducing how often sender-written preview text is displayed to subscribers.

For instance, Gmail’s policy of Automatic Extraction replaces some promotional emails’ preview text with Deal Annotations that the inbox provider automatically applies. In some cases, this results in preview content that is redundant with your subject line, undermines the allure of opening the message, or is simply wrong. While you can control Deal Annotations by adding your own schema coding to your emails, you can’t opt out of Gmail automatically applying schema when you don’t.

At Apple Mail, AI Summaries are replacing sender-written preview text. Enabled by default on Apple smartphones that support Apple Intelligence, AI Summaries use the HTML text in your emails to fuel a generative AI summary of the email. In our experiences, these summaries are rarely more helpful than sender-written preview text. Moreover, like Automatic Extraction, AI Summaries can result in content that’s misleading or outright wrong, leading to poor subscriber experiences.

Given that Gmail and Apple Mail are the two largest inbox providers, with the majority of all emails opened in those two inbox apps, this is a major blow to preview text. These changes make it increasingly risky to write subject lines that rely heavily on the email’s preview text to make sense, such as using the preview text to deliver the punchline for the subject line’s joke or the answer to the subject line’s question.

Related post: Email Annotations & Schema: ‘Automatic Extraction’ & Controlling Your Preview Content 

2. Supplement your subject lines with solid preview text.

While inbox providers are asserting ownership over the preview text space, the preview text you write for your emails will still be seen by a critical mass of subscribers. To make use of this valuable inbox space, consider:

  • Providing more details about the primary message discussed in the subject line, such as price, offer expiration date, the brands available, and the colors available
  • Emphasizing the call-to-action of the subject line
  • Making a value-based appeal if the subject line makes an emotions-based appeal, and vice versa
  • Adding a personalized appeal, if the subject line isn’t personalized
  • Highlighting secondary offers not mentioned in the subject line

Whichever approach you go with, you’ll need to control what appears as your preview text by using either visible or hidden preheader text, which is the HTML text positioned at the very top of the body of your emails.

You may also want to use a preview text hack that allows marketers to create white space that pushes out any unwanted preview text. If you keep your preview text to 20 characters or less, you can use this hack to create a blank line of preview text in some inboxes like Apple Mail. That blank line can make your envelope content stand out even more.

Related post: AI Summaries for Email: Design Impacts on Marketers

3. Subject lines should show contextuality, when it exists.

Automated emails are powerful, with a small but growing percentage of brands generating the majority of their email marketing revenue from these high-ROI messages. These emails are generally sent for one of five reasons:

  1. Action-triggered: The subscriber did something (i.e., abandoned a shopping cart, subscribed to your newsletter)
  2. Inaction-triggered: The subscriber didn’t do something (i.e., hasn’t opened or clicked an email in X days)
  3. Operations-triggered: Something happening operationally that impacts the subscriber (i.e., their order shipped, a product they browsed is back in stock)
  4. Date-triggered: A date approaches that’s important to the subscriber (i.e., appointment reminder, anniversary)
  5. Machine-triggered: One of your brand’s internet-connected products used by the subscriber has sensed something (i.e., low battery, water detected) 

The subject line of your triggered email campaigns should clearly answer the question: Why is the subscriber receiving this particular email? Automated campaigns are as close as you can get to having a one-on-one conversation with your customer via marketing emails. Make your subject line personal. Make it specific.

For example, a subject line like “RSVP successful: See you in Tampa, Susan” allows Susan to clearly connect receiving this email with her registering for the event in Tampa. And since the subject line makes that connection strongly, this email stands out among all the other subject lines in her inbox that are written to appeal to a broad range of recipients.

Sending an automated email immediately after its trigger condition isn’t optimal or appropriate in every case. However, it is for some action-triggered emails such as welcome emails and transactional emails, like the RSVP email mentioned above. That immediacy helps the subscriber connect their actions to why they’re receiving the email.

Make reviewing your subject lines for contextuality part of your regular review and optimization of your automated campaigns.

Related checklist: 110+ Automated Campaign Ideas to Explore.

4. AI can help write subject lines.

Both machine learning tools and generative AI tools can help marketers write subject lines, but each of those functions very differently. Machine learning subject line writing tools use the performance of your past email campaigns and the words used in their subject lines to make word recommendations and predictions. Launched long before generative AI’s mainstream debut in 2022, ML tools like Persado and Jacquard are all about increasing results.

However, the experience of our clients with these tools has generally been disappointing. Without strong guardrails, the out-of-the-box recommendations tend to be very open-baity, which harms subscriber trust. Moveover, positive results are typically short-lived, with performance dropping back down near or at previous baseline levels fairly quickly. Given the price of these tools, that makes positive ROIs challenging to achieve.

Related post: Using AI Subject Line and Copywriting Tools Successfully

Of course, generative AI engines can also be used to write subject lines, whether they’re freestanding tools like ChatGPT or ones integrated into your email service provider explicitly for subject line writing assistance. The key thing to understand about these tools is that they’re about saving time and getting ideas, not increasing performance. Currently, it’s very rare for them to have any information on your past subject lines, your past performance, or even your audience.

So, use these tools accordingly. We find they’re best for brainstorming, generating variations on subject lines you come up with, and doing copyediting, such as reducing character counts. It’s highly likely that any subject line your copywriters write will outperform a subject line written by genAI in a head-to-head A/B test, but these tools can be helpful. Understand their limits and do lots of tests.

Related post: AI-Generated Text: Generative AI Concerns & Opportunities for Marketers

5. Subject lines can include visual elements.

Since the first major inbox providers started supporting them in 2014, emojis have become a common sight in inboxes. Indeed, the novelty has long since worn off, with emojis in subject lines now being as likely to hurt your subject line performance as help it.

With that in mind, the first question you should ask yourself is whether emojis are appropriate for your brand at all, given their relaxed, casual, and even cutesy vibe. If you decide emojis are on-brand for you—even if it’s just for some campaigns—then we recommend creating some usage guidelines.

First, create a list of approved emojis. Which emojis align with your brand? Consider excluding ones that have risque, unsavory, or otherwise NSFW associations (we’re looking at you Eggplant, Peach, and Sweat Droplets). Consider favoring common emoji, particularly those with short, straight-forward names like Red Heart, Star, and Fire (more on that later). And consider checking Emojipedia and other sources to understand the variations in how emoji are rendered across platforms.

And second, establish rules for emoji placement. We find emojis are most effective at the beginning of a subject line, at the end, or in the middle as a separator between two ideas. It’s generally wise to avoid replacing words with emoji. Instead, use emoji as intensifiers to stress certain words or ideas.

Related post: A Year of Campaign Subject Lines

6. Subject lines should be voice-friendly.

The countercurrent to subject lines being more visual is that they’re also becoming more auditory. That’s true of emails in general, as consumers use screen readers and voice assistants to have their emails read to them, whether by necessity or convenience.

Because your subject line is one of the first elements to be read aloud by these apps, it can set the tone for how voice-friendly your subscribers can expect your emails to be. And for voice assistant users who are just using them to triage their inboxes, it can make the difference between your email being saved to read later or deleted.

In particular, the following elements can result in strange and nonsensical subject lines when read by screen readers and voice assistants: 

  • Emojis and special characters. Many emojis and special characters have long, ungainly names that can distract from the message of your subject line.
  • Air quotes. Hip and sarcastic air quotes lose some of their pithiness when voice assistants say, “quotation mark” on either side of the word or phrase.
  • Parentheses. Similar to air quotes, little asides and clever additions sound heavy-handed when “open parenthesis” and “close parenthesis” are uttered around them.
  • Strikethroughs. These can also be awkward when read. However, some platforms ignore strikethroughs entirely, which creates confusing, often contradictory statements.
  • Onomatopoeia. Voice assistants don’t always correctly interpret sound-based words like “Grr” and “Psst,” especially when they’re embellished in any way.
  • Irregular spacing. Particularly in between the letters of a word, extra spacing can cause voice assistants to not recognize words and instead read each letter separately.
  • Acronyms and abbreviations. While voice assistants understand some common acronyms and abbreviations, less common ones can lead to strange readings.

That’s a long list of fairly common and quite fun tactics. Don’t think of it as a ban list, but  rather a be-careful-with-these list.

Related post: Voice Assistants Reading Emails: How to Create Voice-Friendly Campaigns

Despite all of these changes to subject line writing, the goal of a subject line remains the same: to get those subscribers who are most likely to convert to open and engage with the email—and, to a lesser extent, dissuade those who are the least likely to convert from opening the email and being disappointed to the point that they unsubscribe or don’t open future emails.

Generally, that’s accomplished by using descriptive (not vague) subject lines that are focused on what the email is offering the subscriber and are front-loaded with the most important keywords. 

Keep these foundational tenets of subject line writing in mind as you think about how you adapt to these six subject line writing trends.

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Now updated, this blog post was originally published on Aug. 20, 2019 by Chad S. White, with contributions from Lizette Resendez, Kelly Moran, and Monica McClure.