The longer the length (in characters) of a B2C email subject line, the higher its open, click, and click-to-open rates, finds Adestra [download page] in a July 2012 study of 932 million emails from more than 40,000 campaigns across 6 sectors, sent over a 6-month period. The results show that B2C emails have a below-average click-to-open rate (CTOR) for subject lines between 20 and 60 characters in length, but after that pick up steam, hitting their peak at 150 characters in length. These emails have a CTOR 94.7% above the average (and click and open rates 276.4% and 93.2% above-average, respectively). B2B emails show a similar trend, though not quite as clear cut. Emails with subject line length of 20 characters performed above-average for all 3 metrics, though the rates generally dipped after that until recovering from 90 characters in length and up. The peak for open rate was 20 characters (24.6% above-average), while the peak for click rate was for 140 characters (82.7% above-average) and for CTOR was also 140 characters (72% above-average).
E-commerce Emails Show Mixed Trends
Data from Adestra’s subject line study indicates that when it comes to the e-commerce sector, the results are fairly mixed. Subject lines 110 characters in length performed best for open rates (122.4% above-average), but those 70-characters-long did best for click rates (91.1% above-average), while those with 30 characters achieved the best CTOR (17.4% above-average), despite the latter having below-average open and click rates. Overall, subject lines with 70 characters appeared to do the best, with above-average performance in each metric.
For the events sector, short subject lines (20-30 characters) got the highest open rates, while longer subject lines (120-150 characters) got the best click rates and CTOR. Publishing emails displayed the same pattern as events emails, though for charity emails, short subject lines had the highest open, click, and click-to-open rates.
Overall, across the 6 sectors studied, despite an open rate peak for emails with 20 characters, longer subject lines (100+ characters) appeared to deliver better open, click, and click-to-open rates. This compares with recent studies from MailerMailer and Informz, which found shorter subject lines to clearly have the best open rates, though with mixed results for click rates.
Word Count Results Similar
Further results from the Adestra show that word count length has a similar effect to that of character count, but is amplified. Email subject lines that are a single word have a spike in open, click, and click-to-open rates relative to the average, though all metrics dip in response rates alongside increasing word length, until 15 words and longer, when they begin to rise and hit new peaks.
Looking at the results by sector, some interesting patterns emerge. For e-commerce emails, 1-word subject lines had the highest open rate, but 4-word lines had the best highest CTOR relative to the average. For events emails, shorter word counts (2-5) delivered the best open rates relative to the average, but longer word counts (19 and up) delivered both the best click and click-to-open rates relative to the average.
For the publishing sector, the results were clearer: longer subject lines delivered generally higher-than-average open, click, and click-to-open rates, aside from a spike at 2 words. For the charity sector, short subject lines did well for open and click rates, and longer counts (14 words and up) performed worst for click-to-open rates.
In the B2B and B2C sectors, open, click, and click-to-open rates were generally better for longer word counts, though 2-word subject lines performed best overall in the B2B sector.
“Coupon” Fares Worst Among Offer Terms
Notably, the study finds that for the e-commerce sector, the word “coupon” has open rates that are 55.6% below the average for offers emails, with click rates also 85.8% below-average and CTOR 68.1% below-average. This appears to be in direct contradiction to results from an Epsilon study also released in July, which found that the keyword “coupon” was tops for email opens. However, that study only measured the 2011 holiday season, which may explain the discrepancy in results.
According to Adestra, the words “sale” and “% off” performed best in click rates and CTOR relative to the average for offer emails, and also perform among the best for open rates.
- For the events sector, using currency (particularly $ signs), first names, “thousands,” or “millions” can have an uplift for all 3 metrics.
- For the publishing sector, “video” and “exclusive” perform very well relative to the average, while the terms “newsletter,” “research”, “report,” “forecast,” and “intelligence,” all perform significantly below-average.
- For the charity sector, the words “appeal” and “donate” fare poorly compared to the average, while “give” has above-average results.
- For the B2B sector, currency symbols, as well as words such as “profit,” “revenue,” “turnover,” and “referral” perform markedly above-average, while the term “B2B” shows very poor response rates.
- For the B2C sector, “sale,” “% off,” “video,” “exclusive,” and “new” perform best, while “coupon,” “half price,” “free,” and currency symbols are below-average.
- According to a July 2012 report [pdf] from Experian, including the word “exclusive” in the subject line can provide a lift of 14% in promotion mailings (15.9% with vs. 14% without). Similarly, subject lines including “top 10” or “top 5” deliver open rates 13% higher than promotional emails without them (16.1% vs. 14.3%).
- Also per the Experian findings, emails asking customers to rate and review purchased items generate 2 times higher open rates, 39% higher click rates, 22% higher transaction rates, and 32% higher revenue per email.
About the Data: The Adestra study campaigns had more than 5,000 recipients per campaign, but were not limited to large campaigns. The study was conducted across the client basis without regard to list size.