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3 Keys to Optimizing Your Subject Line


See? It’s important to capture your reader’s attention right away. And a good email subject line will help you do just that.

Marketers sometimes invest all of their energy in designing a beautiful email campaign and neglect their subject line. That’s a rookie mistake that we’re here to help you avoid! A strong subject line ensures that your email will actually be opened so readers can engage with the beautiful design.

Create winning campaigns and boost your open rates with these three key steps:

1. Reach the inbox

Every day, 247 billion emails are sent to 1.4 billion readers. (That’s an average of 176 emails per day per person!) Since keeping spam messages at bay is a top priority for internet service providers (ISPs), it’s essential that your messages not get confused with spam. How do you do that?

Avoid the SPAM Folder

Research has shown that the subject line (second only to the email sender name) is one of the primary elements that determine whether an email will be marked as spam. Improve your chances of being read by following these best practices:

  • Use punctuation carefully – Skip exclamation points because they set an aggressive tone and greatly increase your risk of being labeled as “spam”.
  • Avoid capitalizing ENTIRE words – Excessive capitalization is another key characteristic of spam and they’re like shouting at your reader. It’s best to avoid them altogether.
  • Use phrases – Ensure your subject line makes sense when read as a phrase or sentence. Skipping words like “and” and “or” might reduce the length, but they can make your subject difficult to understand (and land them in the spam filter).
  • Use numbers carefully – Don’t use numbers as the first characters in your subject line — it’s a common tactic used by spammers sharing “coupons”.
  • Key spam words – “free”, “coupon”, “urgent”, “100%”, etc. are often considered “spammy” words. Use your creativity to present value to your readers without coming across as phony.

2. Get contacts to open your emails with better email subject lines

Once your email reaches the inbox, use these tips to engage readers:

Make sure your subject line has enough content

Curious about how long your subject should be? Bottom line: be as concise as possible. Brevity allows your recipient to quickly read and understand your message, which will improve your open rates.

In fact, a recent study by Adestra shows that email open rates begin to decline when a subject is longer than 130 characters.

Email Open Rate vs. Subject Length   
Open Rate vs. Subject Length


Use words that connect with readers

Successful subject lines use strong verbs that inspire desire, emotion, empathy or curiosity. Words like: become, take, discover, come, earn or try perform well because they inspire action on the reader’s part. Note that “try” is often a positive substitute for the word “free” when used appropriately.

Personalize content to the individual recipient

Personalizing your email subject line with the reader’s name or other unique information is proven to increase open rates. According to a Retention Science study analyzing more than 260 million emails, the average open rate for personalized emails (18.3%) was nearly 3% higher than those without personalization (15.7%).

Since most companies (approximately 70%) don’t personalize emails, this is a key opportunity to stand out in the inbox. When including a recipient’s name or other information for personalization, use a friendly, approachable tone.

Sendinblue makes personalization easy by allowing unlimited custom fields to be associated with your contacts. That means you can capture and store helpful data and use it to personalize future messages.

3. Encourage action

Once you’ve captured your reader’s attention, it’s important to discourage procrastination by conveying a sense of urgency or offering a solution to a problem.

Create Urgency

When a message is time-sensitive, ensure this is clear in your subject line. For example, if your offer is only available for the next three hours, make sure your reader knows so they don’t push save it for later.

Offer a Solution

If your email subject promises a solution to a real issue they are experiencing, the reader will open it quickly. If you can help replace a stolen key, reset a lost password, or something similarly useful, be sure to communicate your value proposition in your subject line!

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3 Keys to Optimizing Your Subject Line

time to read: 3 min