Brevity may be the soul of wit but not so the B2C e-mail subject line. As reported by Marketing Charts, a July study from Adestra found that the longer the length (in characters) of a B2C e-mail subject line, the higher its open, click and click-to-open rates.
The study looked at 932 million e-mails from more than 40,000 campaigns across six sectors, sent over a six-month period. (The 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.) The results show a below-average click-to-open rate (CTOR) for subject lines between 20 and 60 characters in length. As the number of characters grows, the rates pick up steam, hitting their peak at 150 characters in length. These e-mails have a CTOR 94.7 percent above the average, click rates 276.4 percent above average and open rates 93.2 percent above average.
B2B e-mails show a similar trend, though not quite as clear-cut. E-mails with subject-line length of 20 characters performed above average for all three 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 percent above average), while the peak for click rate was for 140 characters (82.7 percent above average) and for CTOR was also 140 characters (72 percent above average).
E-commerce results mixed
In the e-commerce sector, the results are fairly mixed. Subject lines 110 characters in length performed best for open rates (122.4 percent above average) but those 70-characters long did best for click rates (91.1 percent above average), while those with 30 characters achieved the best CTOR (17.4 percent 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-related e-mails displayed the same pattern as events e-mails, though for charity e-mails, short subject lines had the highest open, click and click-to-open rates.
Overall, across the six sectors studied, despite an open rate peak for e-mails 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. E-mail 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 e-mails, one-word subject lines had the highest open rate, but four-word lines had the best highest CTOR relative to the average. For events e-mails, shorter word counts (two to five) 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 two 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 two-word subject lines performed best overall in the B2B sector.
“Coupon” fares worst
Notably, the study finds that for the e-commerce sector, the word “coupon” has open rates that are 55.6 percent below the average for offers e-mails, with click rates also 85.8 percent below average and CTOR 68.1 percent 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 e-mail opens. However, that study only measured the 2011 holiday season, which may explain the discrepancy in results.
According to Adestra, the words “sale” and “percent off” performed best in click rates and CTOR relative to the average for offer e-mails, and also perform among the best for open rates.
In other findings:
- For the events sector, using currency (particularly $ signs), first names, “thousands” or “millions” can have an uplift for all three 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,” “ percent 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 percent in promotion mailings (15.9 percent with vs. 14 percent without). Similarly, subject lines including “top 10″ or “top 5″ deliver open rates 13 percent higher than promotional e-mails without them (16.1 percent vs. 14.3 percent).
- Also per the Experian findings, e-mails asking customers to rate and review purchased items generate two-times higher open rates, 39 percent higher click rates, 22 percent higher transaction rates, and 32 percent higher revenue per e-mail.