Email marketing subject lines: 6 guidelines & best practices

Estimated reading time: 5 minutes

Email is one of the most budget-friendly marketing tactics available to small businesses, but it is only effective when your customers click and read. With 35% of email recipients stating that they’re influenced by email subject lines, why not focus on making those subject lines as catchy as possible?

The subject line of your email is your first impression on recipients. Its importance is similar to the first few words of a Facebook caption, or the back cover of a novel. It’s the virtual equivalent of a knock at the door or an elevator pitch. When done right, email subject lines can get your audience to stop what they’re doing and open your message.

Here, we’ll go over everything you need to know about email subject lines and strategy.

First, think about how you’ll measure success.

If you’re sending multiple emails and using subject line variations, how do you know which are succeeding—and which aren’t? The answer lies in knowing what key performance indicators (KPIs) to measure to determine your email marketing return on investment (ROI). Depending on your business goals, certain KPIs will serve as a better measure of success than others.

The following KPIs commonly reflect recipient engagement and the overall performance of an email campaign.

• Open rate: The open rate is calculated by dividing the number of emails opened by the number of emails sent, then multiplying the answer by 100. So if you send 10 emails, and only two are opened, your open rate is 20%. As per HubSpot’s benchmark report, the average email open rate was around 20% across all industries. So, an open rate below this rate suggests that your email subject lines aren’t performing well. Try different variations to see what resonates with your audience.
• Click-through rate (CTR): CTR is calculated by dividing the number of clicks within opened emails by the number of emails sent, then multiplying the answer by 100. According to HubSpot, the average email CTR across industries is 7.8%. Small businesses with a low CTR should experiment with different subject lines and call-to-actions to see what variation generates the most clicks.
• Spam complaint rate: You get this number by dividing the total number of spam complaints by the total number of emails sent, then multiplying the answer by 100. Your spam complaint rate should be lower than 0.1% at any given point. That equals 1 spam complaint per 1,000 emails sent. If you’re experiencing a high spam complaint rate, it could mean that your subject lines are coming off as spammy to your recipients. The solution is to make them personal and compelling.

Next, review the best practices for email subject lines.

Spending some extra time crafting your email subject lines can help you increase open rates, get more clicks and avoid the spam folder. Use the following 5 strategies to give your emails an edge.

1. Add a personal touch.

Personalizing your subject lines is a great way to get your emails opened, and it can be as simple as using the first and last name of the recipient. You can also weave in birthdays, location and other preferences to pack a stronger punch. Small businesses that take this route can save time by setting up an email series (multiple email messages that will be sent to people on a schedule automatically) with personalized subject lines through their email service provider. So, when it’s someone’s birthday, they’ll automatically get a personalized email with a subject line like, ‘Happy birthday, Julia! Your gift is inside.’

2. Demonstrate value.

Play up the utility card first before using sales-oriented communication. Showcasing exactly what value the email offers is a powerful way to stand out in a cluttered inbox. As an example, the subject line ‘Carlo’s Cafe customer-favorite menu hacks’ gives an indication that the email is resourceful, and is likely to appeal to any foodie on your mailing list.

3. Use action verbs.

Use action-oriented verbs to grab attention…and trigger a specific next step. For instance, an email subject line that says “Sign up to receive invites for our calendar event” is likely to be more effective than “Our calendar event is going to be exciting,” especially if you’re trying to drive sign-ups for your event. Action verbs like “sign up,” “enroll” and “download” create a sense of urgency and curiosity, prompting recipients to check out your offer.

4. Play with an emoji (or two).

Dressing up your email subject lines with emojis is a unique way to grab people’s attention. A contextually relevant emoji can add great value to your subject line, which will boost your open rate. However, emojis should be used purposefully. If your subject line is about a discount or exciting news, add a smiley face with sunglasses or hearts. If the subject line is serious—for instance, something related to loss of customer data—skip emojis altogether.

5. Ask a question.

What better way is there to engage with someone than by asking them a question? You can take this approach to your subject line strategy and pose a question to subscribers. Something like, ‘Which sale styles will you grab?’ or ‘Which flavor will you choose?’ is a great way to grab the reader’s attention and get them to open your email.

6. Keep it brief.

Your subscribers will be reading your emails on their phones and their computers…so keep mobile devices in mind when you’re writing subject lines. You want to make sure the whole line is visible on their screen, so aim to keep your message under 40 characters. If you’re struggling to keep your subject line short and sweet, prioritize the most important words or key message. For example, instead of saying ‘We have some exciting news to share about our uptown location!’ try ‘News for uptown shoppers inside!’

7. Avoid email spam filters

First things first: your email needs to actually make it to the reader’s inbox before it can be effective. While it’s understandable why some emails are immediately marked as spam, a few surprising practices can also trigger the journey to the spam folder. Follow these tips to ensure your emails don’t get flagged.

• Avoid using ALL CAPS, as it gives an illusion that you’re shouting at the reader.
• Avoid excessive usage of asterisks and punctuation as they can make your subject line appear unprofessional.
• Avoid words that are known to flag spam triggers, such as “free offer,” “lotto winner” and “save $.” Here’s a detailed list of common spam words.
• Don’t send emails with one-word subject lines. They don’t convey value.
• Don’t trick recipients by using “fwd:” or “re:” at the start of your email subject lines to suggest ongoing communication.

Now, craft a subject line that speaks to the email’s content.

The subject lines of promotional emails, newsletters and announcements will be different—both in content and in tone.

If your business sends out a regular email newsletter, subscribers will come to expect it. So, make it clear that these emails are part of a series through the subject line. For example, ‘New at Sara’s Styles: the March Lookbook.’ Or, ‘Clarendon Consulting Weekly Digest.’

Putting together an email to announce some exciting news? Draw people in with the subject line—this is your chance to use a capitalized word or a fun emoji. If you have major news to share, you can keep your subject line pretty simple. Something like ‘Our new location is open!’ or ‘Now open late!’ is all you need.

If you’re creating a promotional email, the subject line should clearly speak to that. They should know the benefits of the email without even opening it…but they’ll be so excited by the offer that they will click through. Consider subject lines like ‘Free shipping on your next purchase,’ ‘Come back and save 15%’ or ‘Inside: Gift with purchase’ to intrigue and excite your customers.