Are You Using the Right Email Subject Line Words and Phrases?

Effective Email Subject Lines

The subject line of your email is either going to get your email opened or ignored. Because messages can either turn on or turn off your recipients with just one word or phrase, look closely at the wording of your subject lines.

Yes, you CAN make a break a connection with just a word. Want to know what some of those words are? You’ll be surprised. 

Marketing firm Adestra analyzed a sample of more than 125,000 individual email campaigns, 3 billion attempted sends, 400 million opens, and 55 million clicks, Adestra tracked some of the more common keywords and phrases across four industries to see how they fared by viewer responses. The results were reported in

Content-related terms are among the top 10 words that crossed industries in above-average response rates, according to Adestra, those words that reflect benefits rather than features for the customer. Adestra also expressed these caveats:

  • No single word is always going to work all of the time.
  • Many terms that performed well in open rates performed badly in click rates and vice versa.
  • Some results appeared confusing and inconsistent with previous research.

What follows are above-average, below-average and inconsistent response rates for some of the more popular terms used by industry. The data comes mostly from the UK, so take geographic variances into account.


Above average:
“10% off” and “25% off” (for open rates)
“50% off”, “25% off’ and “10% off” (for click rates)

Below average:
“15% off” and “50% off” (for open rates)

While “50% off” was above average in click rates by 33%, that same phrase was -7% in open rates. “25% off” was the only discount term to perform better than average for both opens and clicks. Another finding was that personalized emails were below average in open rates (-30%), click rates (-20%), and unsubscribes (+9%).



Above average:
“advice,” “buy,” “save” (for open and click rates)

Below average:
“agenda,” “forum,” “keynote,” and “speakers” “come,” “early bird,” “free,” and “register”  (for open and click rates)

“Keynote” was staggeringly below average (-259%)! The word “advice” had an open rate of +6%) and a more significant rise in click rate of +27%.

Media and Publishing

Above average:
“breaking” (35% open rate and 66% click rate)
“exclusive” (15% above-average open rate; 7% above-average click rate);
“review” (24% open rate and 61% click rate);
“top stories (28% open rate and 58% click rate)
“on sale now” (27% open rate and 57% click rate)

Below average:
“25% off” (-7% open rate and -65% click rate)

“free” and “order today” did well in one metric but not the other.

B2B/Professional Services/Financial

Above average:
“news” (the only popular term in the above-average category (open 33%, click 40%)
“bulletin,” “interview,” “industry” (good for unsubscribe rates)
“asset,” “discount” (bad for unsubscribe rates)

Below average:
“whitepaper” (open rate -208%, click rate -402%)
“alert” (-105% open rate, -353%, click rate)
“forecast” (-149% open rate, -270% click rate)
“download” and “report” (below-average rates but closer to average)

Subject Line Length

In a different study measuring line length and response rates, MailerMailer found that 4-15 characters had the best open and click rates; longer subject lines reflected lower open and click rates.

The data was based on 62,000 newsletter campaigns and 1.18 billion email messages sent. The results tracked only marketers with 25 or more list members and excluded emails with no links.


  • Use words that reflect benefits rather than features.
  • No single word is always going to work all of the time.
  • Research words that increase and decrease response rates by industry.
  • Use shorter line lengths for your subject lines.