Inbox Pros Blog   »   How to Develop a High-Open Rate Subject Line

April 3, 2017

How to Develop a High-Open Rate Subject Line

Author | Brittany McCusker

  1. Intro: Why We Need Great Subject Lines
  2. Your Subject Line’s Deliverability
  3. Spam Filters: Subject Lines to Avoid
  4. Importance of Personalization
  5. Data-Driven Subject Line Keywords
  6. Use of Greed Factor
  7. To be ‘Free’ or not to be ‘Free’
  8. Fear of Loss
  9. Emoji’s in subject lines
  10. Conclusion


Intro: Why Great Subject Lines are Important


Did you know that 47% of recipients decide if they are going to open their email based on subject line alone? That’s a large percentage of decision-making. Another note is that 69% of recipients report email to spam based solely on subject lines. As an email sender your top priority should be staying out of the spam folder. What most don’t realize is that if your emails are being sent to spam enough times, your sending reputation decreases and then you’re already on the road to being blacklisted as a sender. This is not something you want, because then you will have to start working on building your reputation back versus working on content for your prospect. That is why it’s uber important to understand and follow best practices when sending email.


Your Subject Line’s Deliverability


Deliverability is the success at which an email is delivered to a recipient’s inbox. When developing a high-open rate subject line the first thing to understand is that your email must be ‘delivered’ before it can be ‘opened’. It is not as simple as ‘click’ and done. Once an email’s been sent it’s filtered through several spam filters, authenticated through DMARC, and other ISP, ESP, and blacklist filters before it’s delivered into your recipient’s inbox. The goal of email service providers is to provide a pleasant experience for their users with other users, not for them to be bombarded with junk mail. Therefore, if your subject line looks like junk mail to ISP’s then your email will not be delivered. Sounds straightforward enough, right? Unfortunately it’s not. ISP’s are constantly changing what they identify as ‘spam’ therefore keeping up-to-date with this needs to be part of your sales and marketing cup sitting on table with marketing information


Spam Filters: Subject Lines to Avoid


Before we talk about what to do when developing your subject line. We first need to talk about what to avoid doing. By putting the wrong text in your subject line you can be caught by spam traps. A “spam filter” is a filter that’s used to detect unwanted email and prevent those messages from getting to a user’s inbox. Like other types of filtering programs, a spam filter looks for certain criteria on which it bases judgments. Here is a list of 438 Email Spam Trigger words to not use when sending emails to your prospects. A subject line best practice is to peak a reader’s interest, but not sound salesy.


Importance of Personalization


A subject line is the first impression that your prospect has of you. We all know first impressions last, so that is where personalization comes in handy. Several studies have concluded that Baby Boomers, Generation X, Millenials, and iGens in 2017 interact most with brands that use some sort of personalization in their communications. When speaking to someone using their name can be the sweetest sound to their ears. To imitate this with email use effective personalization by adding {First-Name} & {Last-Name}, or even {Company-Name} into your subject line. A study conducted by MailChimp showed that using a recipient’s first and last name in the subject line had higher open rates than only using first or last name.

One vital best practice for personalization is understanding your prospects buyer persona and where they are in the buyer’s journey. Sending someone the wrong message at the wrong time will definitely not get opens and could potentially get them to mark your brand as spam. A 2015 Subject Line Study by Experian Marketing Services provided data that showed email subject lines that included the recipient’s name increased open rates by 23.8%. Names are only one way to get higher open-rates. You can try using familiar language that implies a friendship, be casual, or share something personal.

Ever wonder why some emails your receive are more enticing to open than others? Even if you don’t open emails from that brand that often? It’s because they personalized their message for you. By peaking a recipient’s interest to open, you will develop a high-open rate subject line. Start by asking yourself who they are? What are they interested in? What is their goal in business? In life? How can you grab their attention by talking to them like a friend? If it was you on the other end, would you open your message when putting yourself in their shoes?


Data-Driven Subject Line Keywords


Here’s the thing: if people don’t open your email, there’s a 0% chance they will see your creative. When developing your subject line it’s important to know which subject lines have had a history of working and which have not.


Alchemy Worx did a study from 24.5 Billion subject lines, identifying The Five Most Effective (and Ineffective) Words in Email Subject Lines. This study concluded which words had higher open rates and which words had the least effective open rates.

Digital Marketer’s study of 101 Best Email Subject Lines of 2016 analyzed over 125 million subject lines and concluded that marketers should try using these phrases in their subject lines.

  • “Get this now”
  • “Is coming”
  • (use numbers in your subject line) Example: “5-step plan”, “3 week course”, “101 ideas”


Adestra explains how to Improve your subject lines like never before by saying ‘Thank You’ in your subject line. Adestra’s study showed that 62% of recipients opened their email after seeing ‘Thank You’ in the subject line. This study also shows that “*|*|*|*|” had an open rate of 47%. Other high open rate subject lines were:

  • “Monthly” -45%
  • “Thanks” -34%
  • “Bulletin” -32%
  • “Golden” -30%
  • “iPhone” -30%
  • “Breaking” -27%
  • “Order Today” -27%


Ask Them a Question


Questions provoke answers. When asking your recipients a question ask them about their pain points, business goals, personal goals, or questions that you would want answered if you were in their shoes. If you ask the right question you will entice recipients of your email to click and therefore have a high open rate subject line. In Litmus’ study on How To Write The Perfect Subject Line, it was found that subject lines phrased as questions performed better than some similar phrased as statements.


In the same study it was shown that shorter subject lines performed better as well.


Use of Greed Factor


Have you ever heard the expression “keeping up with the Jones”? What this expression means is that psychologically everyone wants what everyone else has. Even if that person isn’t going to use the item. Again, knowing your audience is key to understanding their desires. Knowing your buyer persona is key.

Here are some example subject lines:


  • Topshop: “Meet your new jeans”
  • Topshop: “Get a head start on summer”
  • HP: “Flash. Sale. Alert.”
  • HP: “New must-haves for your office”
  • Seafolly: “A new product you won’t pass on”
  • Guess: “25% off your favorites”
  • Rip Curl: “Two for two”
  • La Mer: “A little luxury at a great price”
  • Rapha: “Complimentary gift wrap on all purchases”
  • The Black Tux: “Get priority access.”


If someone else is grabbing it, then automatically our curiosity or skepticism will get the best of us. We can use this strategy when developing our subject lines. It’s also hard to pass-up a good deal. Be careful though because if you give too high of a discount, most consumers will think it is fake and some wording can get you sent to the spam folder.


“Only here a limited-time”, “don’t want you to miss out”, and “last day/week” are a few of many phrases that emphasize a fear of loss. Studies show that subject lines with a time-sensitive appearance are proven to be seen as important and urgent. You can use this strategy in your subject lines by adding an element of scarcity (limited availability) or urgency (limited time). Subject Line Data: Choose Your Words Wisely is a study from MailChimp that concludes urgent words increased open rates.


To be ‘Free’ or not to be ‘Free’


MailChimp also conducted a study showing that the use of the word ‘free’ in subject lines can have a drastic impact on open-rates depending on which industry you are in.


Thinking about using symbols in your email subject lines? You may want to because according to a study from Experian, using emoji’s in your subject line can increase your open rate by 45%. Be careful when choosing which emoji to use and make sure they are going to render properly on all ISP’s. You don’t want your subject line to have the ▢ symbol. This symbol may trigger a spam filter and block you from inbox placement. Below you can see a test performed by Campaign Monitor. With the exception of Outlook 2003, they found all email clients to support emoji’s. You can find out more about Using Emoji and Symbols in Your Email Subject Lines in this link to Campaign Monitor.


All in all, your email’s deliverability is the most important first step you should take when developing your subject line. Find out what spam traps are and keep updated on spam trap keywords. You don’t want your content to get triggered, not seen, and sent to spam. It is vital to keep subject lines and anything sales and marketing related personalized. Know your buyer persona and their needs as a person so you are able to spark their interest. Use numbers in your subject line and if you’re using a discount try a lower discount number. Larger numbers can get caught in spam filters and often people see too high of discounts being fake anyways. Using the word “Free” will get you higher open rates in some industries while others can get you sent to spam from users. Be careful to not lower your sending reputation by not being educated in this area. Use fear of loss. If there is a scarcity in an item’s quantity or time being around, this will spark importance and urgency from your recipient. Also, try Emoji’s in subject lines. It is proven that they will increase open rates up to 45%.


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