7 Best Practices for Successful Email Subject Lines In 2024

Like most digital marketing industry averages, the criteria for “good” and “successful” email marketing changes often.

Is your open rate above 21%?

Is your click-through rate below 35?

(For more information on where your email marketing numbers should be, check out this handy blog.)

Then, there’s the all-important deliverability question: How’s your spam score? 

With spam filters constantly advancing, digital marketers need to know what triggers spam filters in order to increase email deliverability and land in inboxes. That’s only half the battle, though.

Email marketers also need to stay on top of your subscribers’ behaviors and interests in order to continue getting opened, because engagement (clicks, forwards, and replies) affects deliverability.

Both avoiding the spam filter and getting a campaign opened relies heavily on your subject line. It’s the first thing your subscriber sees in their inbox.

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With that in mind, here are the top email subject line best practices for digital marketing:

1. Keep them short

Successful email subject lines should always be concise. Think of your email marketing campaign as breaking news, which means your subject line is the big bold headline.

Prioritize summarizing what’s in the email and why people should click. If you’re able to add a clever or creative twist (or even an emoji) without jeopardizing the length or integrity of the message, then go for it!

Another email marketing best practice? Always use the preview text. This is a great way to elaborate on the subject line.

2. Don’t use spammy words

Email marketing builds trust between your brand and subscribers. If your readers feel like your content is “spammy” or misleading, you risk being reported, sent to the junk folder, and notching higher spam and unsubscribe reports.

This is because a subject line often functions as a call-to-action. It inspires urgency or curiosity, but some words (475 to be exact) must be avoided. Stay away from words that could be described as shady, cheap, far-fetched, manipulative, needy, or sleazy.

Use this quick list that will definitely trigger spam filters to flag your email as suspicious:

• As seen on
• Do it today
• What are you waiting for?
• Order now
• Click below
• Bargain
• Best price
• Free (gift)
• Satisfaction guaranteed
• Incredible deal
• Act now
• Apply now
• Instant
• Limited time
• Urgent
• Earn extra cash
• Free money
• No hidden costs
• Risk free
• No fees
• Score
• Social Security Number
• Spam
• Unsolicited
• Warranty
• No purchase necessary
• Winner
• Free info
• Free membership
• Dramatically reduced

Email Marketing Tip: On the topic of spam, don’t write your subject line in all-caps. You’re basically yelling at spam filters to flag your message.

3. Don’t lie or mislead

The goal of email marketing is to build a rapport with your subscribers. Don’t jeopardize that trust by making a false promise in your subject line.

It may increase opens for that specific campaign, but your subscribers will feel irritated and misled. They’ll take it out on your future email campaigns by deleting them, flagging them as junk mail, or never opening them.

Because spam filters account for the engagement of your previous campaigns, these actions can seriously harm your email marketing efforts. Honesty is the best policy.

4. Ask questions

When executed properly, questions are examples of great subject lines. They often pique interest, and curiosity inevitably leads to an opened email.

So, how do email marketers properly execute a question as a subject line? Think about how your product or service could benefit the subscriber. Frame the question around that, like these email subject line examples:

For newsletters, think about the overall question your main content answers, and ask that question as the subject line. Per usual, it’ll pique the curiosity of your email subscribers like these email subject line examples:

5. Include deadlines

Be careful about inciting a sense of urgency with your subscribers. Don’t be misleading or fearful. It’s completely fine when it’s not aggressive, like mentioning that a sale ends tomorrow or counting down the days until a new product’s release or restock. These deadline-forward subject lines can successfully inspire your subscribers to open and/or click without triggering a red flag from spam filters.

6. Personalize

Thanks to email list segmentation, you can go beyond including just your subscriber’s name in the subject line. (Although that works well, too. Personalization over generalization every time.)

You can group subscribers by shopping behavior, geographic location, birthday, interests, age, gender, job industry, and so on. List segmentation allows you to send super-specific campaigns with super-specific email subject lines.

This best practice will ensure high open, click-through, and click-to-open rates, as well as low unsubscribe rates and the all-important low spam score.

‍7. Use a number (or two or three)

Go to your inbox right now. There’s likely an email with a subject line that includes a number. It’s the easiest way to create a good subject line. (In fact, it’s a best practice taken from content marketing for blogs.)

If it’s not a discount or price, the number is probably part of a list.

Numbers help capture attention, because they stand out among the sea of letters. Plus, content presented in a numerical list format is easy reading for most subscribers, which makes these emails highly clickable without being click-baity.

Lists are great for newsletters and emails that contain blogs. They also work well for promoting products and services, like Uncommon Goods (www.uncommongoods.com) does here:

If you have the opportunity to use a number in the subject line, take advantage. Save those AP Style rules for blogs when it comes to dates, prices, discounts, days/hours remaining, and  more.

Using numbers in emails will also save you precious character counts within the subject line. Short and sweet, number-driven lines grab subscribers’ attention and subsequently increase the email campaign’s engagement. This helps boost deliverability for future campaigns.

To wrap it up

Like sender names, subject lines can both negatively and positively impact your email marketing campaigns. These best practices are generally successful, but to ensure they work for you, it’s important to keep an eye on your analytics and A/B test. The open and click-to-open rates from subscribers will let you know whether your subject line has truly succeeded.

To learn more about the basics of email marketing, download A Beginner’s Guide to Email Marketing by Mirabel’s Marketing Manager. Click on the button below to download your copy: