Subject Line Optimization -  A Guide to Boosting Open Rates

The subject line and Email preview is the first impression of your Campaign on your Email recipients. The subject-line is important consideration for unique open rates. There is a lot of literature on the topic, so what follow are our tips:

Avoid Sounding Desperate 

  • Avoid Spam-Filter alert words such as the following: free, sale, help, percent off, reminder, etc… (for other top hits to ignore Click here).
  • Do not use symbols in the subject-line (for more info Click here)

Shorter Subject Lines is Better

  • 50 characters including spaces should be the limit! This is one of the golden rules.
  • For a genereal purpose blast go short, for a very targetted segement, be as specific as possible in a longer subject line.
  • For Promotions, try subject-lines with questions

 Subject Line Techniques 

These techniques are cited as boosting open-  rates:

1) List Email Subject Lines (“10 Win-Win Strategies for Quitting Your Job”)

Trait: Inspire Self-education 

2) Ask a question

Trait: Evoke curiousity 

3) Use the phrase “Reasons Why….” (e.g. “5 Reasons Why You Should Use the Reason  Why Subject Line Template“)

Trait: Informative Hints

4) State the Benefit of the CTA in the subject line. Emphasize the benefit over the features. These sometimes include an implied promise.

e.g. “20 Country Slow Cooker Recipes” that when turned into a benefit subject line, “Top 10 Lazy Skillet Meals” zoomed from an 18.2% to 19.6% open rate.

Trait: Usefulness

5) Testimonial Insert Subject Lines (.e.g Tiger Woods Can Afford any car; He Drives a Buick)

Trait: Infuencer credibility 

6) How-to Email Subject Lines (.e.g “How to Make a Fortune with a Foolish Idea“)

Trait: Promote interest 

For more of these see here.

Subject Line Optimization Test (SLOT)

So this is our own invention here at eFlyerMaker, your subject-line should be salient in one of the next 3 points & not break one of the 4 things to avoid:

Ask yourself, does your subject line present:

1) Timely information that allows for immediate benefit of the person

2) Personal with high affinity for a person’s preferences: sent to a segement that is grouped by personal interest!

3) Provide immediate required information (tracking, updates, product bought, triggered message, info on registration, etc..)

In that, the best subject lines cater to either immediacy, personalization or triggered information by a customer’s actions.

At the same time the SLOT manual says you must avoid the following:

1) Subject line is over 50 characters (unless it’s a highly targgeted segement)

2) Subject line uses CAPS or special characters

3) Spam word “Help” is used here which will ellicit igornes and spam-clicks

4) The subject line Over Promises (too good to be true)

Here, the literature suggests we avoid lengthy, attention-seeking punctuation, begging & pleading and over-trying subject lines

 Creative Ideas

Test & consider the following:

  • Placing a CTA in the subject-line itself
  • Placing ‘ambiguous‘ or ‘cheeky’ text in the subject lines
  • Creating “personas” for your customer segements and brainstorm together what kind of subject line would most entice different kinds of people to read further (make focus groups). If you don’t have personas already profiled, consider by gender and age.
  • Insert Subject lines that stand out, bordering on the unusual.
  • Write subject-lines based on the device trends your recipients are opening their Emails on:

Longer subject-lines for Segements where Android users are high, since they spend more time on each message on average. Shorter subject lines for Apple lovers.

  • Write your subject lines assuming mobile reads, as it’s becoming clear more than 50% of view are now from mobile (mainly Apple) devices:

If you do a location based blast via Postalcode and City, link it with current events or in other ingenius ways of topics that are known to have high open rates for mobile devices:

Keywords of Subject Lines 


- Don’t use any language or words that could be interpreted as spam sales lingo (be careful with repetitive use of subject lines, or action-words)

- Be human & honest, the subject line ought to be warm and it should not read as a triggered message


- Be concise and demonstrate objectivity

- Describe the point of the email message


- Match their preferences to the subject line

- Create a time-bound sense of immediacy

Brainstorm on your Brand’s Unique Selling Proposition 

Your BUSP (brand unique selling proposition) is the central thing that makes your product, service or brand exceptional. Your subject-line should in a way, encapsulate that in different ways:

  • Think about your Brand’s logo, motto and create powerful subjet lines from there
  • Do you have a keyphrase or key values that you can incorporate in the subject line?
  • What can you do in your Email Design that stands out that you can give a mention to in your sujbect line?
  • What makes your product unique and better than your competitors’ products?
  • How can you present your service to inspire people to want to click, open or buy?

Subject Line Hacks

Micros Subject Lines (MSL)

1) Micros Subject Lines tend to perform well according to some evidence: subject lines with 6-10 words had the highest open rate, and subject lines with words in the 0-5 range had the second highest open rate.

Because mobile devices display fewer characters of a subject line than their webmail and desktop email client counterparts, the growth of mobile email reading is putting downward pressure on subject line lengths.

First Name Basis Personalization (FNBP)

2) Personalizing the first name of the subscriber in the subject-line as the first word, still works.

Hybrid Subject Lines (HSL)

3) This is the practice of mentioning 2 highlights about your Email blast, instead of just one. This can sometimes get more opens, since the 2nd mention may be more suited to the person:

Including multiple topics in your Email subject line, isn’t for everyone, but some firms can make it work for them.

Product Matching Subject Lines (PMSL)

4) Here you take simliar products to those that segement has bought already, and place a promotion to them directly in the subject-line. You assume here that simliar products may interest the recipients, i.e. a customer niche. This of course, assumes you can create segements according to purchasing history. It’s ideal for ecommerce.

If you have a Marketing automation platform, tweak the subject-line to the personalized one-to-one offer to a style of language that correspondes to the gender, age and purchasing history of that person.

APPENDIX of Acronyms

BUSP Brand Unique Selling Proposition What makes your brand or products stand out from the rest!
FNBP First Name Basis Personalization Using first name of recipient as first word in Subject line
HSL Hybrid Subject Lines Using more than one topic in the sujbect line
MSL Micro Subject Lines Using a minimal number of characters to peek interest
PMSL Product Matching Sujbect Lines Using similar products to purchasing history of target segement in the subject line to entice opens
SLOT Sujbect Line Optimization Test Guides to follow to create an optimally performing subject line
SLT Subject line techniques Specific things to say in the subject line

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s