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Email Subject Lines: Which Terms Work, and Which Don’t

by MarketingCharts staff
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Adestra’s study scores keywords by relative open, click, click-to-open, and unsubscribe rate. As such a result of 20% should be read as “20% higher than the average.” (In other words, if the average were 20%, the open rate would be 24%.) This article focuses on open, click, and click-to-open rates only.

(Adestra rightly cautions that “lists may respond differently to the long-run averages” contained in the report, though the results should provide ideas on what should be tested.)

Below, a summary of the results by theme.

B2B Publishing

  • Content: Subject lines containing the “alert” keyword had far better-than-average open (57.8%) and click (32.9%) rates, though click-to-open (CTO) rates were only 2.1% above-average. By contrast, “newsletter” had below-average open (-11.2%), click (-52.6%), and CTO (-46.7%), with “report” and “top stories” also below-average in each metric. The researchers note that content marketing terms may be saturating consumers, and that marketers should focus on differentiation. Content terms such as “breaking” and “editor” saw strong rates, easily above-average for each metric. Also of note, subject lines with multiple stories delineated by pipes (*|**|***) achieved above-average open (27.5%), click (90.7%) and CTO (14.2%) rates.
  • Date: These were a mixed bag. “This Week” and “monthly” both fell below-average in each of the 3 metrics, while “weekly” was above-average in opens (27.5%) and clicks (24.7%) but below-average in CTOs (2.2%). The only date term to be above-average in each metric was “daily,” which sported an open rate 12.6% above the average, a click rate 35.8% above-average, and a CTO rate 20.7% above-average.
  • Subscriptions: These tended to fare more poorly than content or date terms. “Access” (-9.9%), “free” (-11.1%), “renew” (-21.9%), “subscription” (-15.8%) and “trial” (-14.1%) all saw below-average click-to-open rates, with each of those save for “renew” (22.6%) also below-average in click rates. At the same point, they each sported above-average open rates, except for “subscription” (-8.2%). In fact, “subscription” was below-average in each metric. Only subject lines containing the £ symbol performed above-average in all 3 metrics, and that’s obviously subject to targeting, as the symbol may be irrelevant to many recipients.

B2C Publishing

  • Content: Unlike with B2B publishers, subject lines containing the the term “newsletter” saw above-average open (6.4%), click (16.5%) and CTO (9.5%) rates. But, that was overshadowed by the stronger performances of subject lines containing the terms “video,” and “review,” along with those with multiple stories delineated by pipes, or commas. Subject lines containing the question mark symbol fared the worst, with open (-16.9%), click (-22.2%) and CTO (-6.4%) rates all below-average. The term “special” had below-average click and CTO rates, but above-average open rate.
  • Date: As with B2B publishers, the term “monthly” did not fare well, below-average in open (-4.9%), click (-24.6%) and CTO (-20.7%) rates. “Daily” was easily the top performer, scoring way above-average in open (35.1%), click (115%) and CTO (59.2%) rates.
  • Money: These generally tended very poorly. Subject lines containing the £ symbol were below-average in each metric, as were those containing “free,” “% off,” and “discount.” Only “half price” managed to stay above-average in open rates (9.7%), although it also fell behind in click (-44.1%) and CTO (-49.1%) rates.
  • Subscriptions: If the data is to be trusted, B2C publishers should avoid “last chance”, “subscription,” and “trial,” keywords in their subject lines, with each of these below-average in the 3 metrics tracked for this article. (“Trial” was by far the worst performer, with a click rate 74.6% below the average. “Limited” saw above-average open (23.7%) and click (16.4%) rates, but below-average CTO (-5.9%) rates, while “on sale now” was slightly below-average in open rates, but slightly above-average in click and CTO rates.
  • Miscellaneous: B2C publisher emails containing the term “Twitter” performed above-average in open (12.2%), click (18.1%) and CTO (5.3%) rates. “Facebook” was not as lucky with open rates (-6.7%), but also fared better than the average in click (15.2%) and CTO (23.4%) rates. “Deals” performed relatively well in opens (7.3%), but dropped below average in click (-12.3%) and CTO (-18.3%) rates.

B2B Events

  • Product: These tended to fare poorly, with “conference,” “forum,” “training,” and “webinar,” each seeing below-average rates in the 3 metrics. Only “exhibition” escaped that fate with a CTO rate 7.5% above-average, although it was below-average in open (-8.2%) and click (-1.4%) rates.
  • Discounts: “Early bird,” “discount,” and “offer” were below-average in open rates, but really tailed off in click and CTO rates, at roughly 30% or more below-average in those metrics. “Free” saw a slightly below-average open rate (-3%), but jumped ahead of the average in click (3.7%) and CTO (6.9%) rates.
  • Urgency: Simply put, the data shows that “Don’t miss” is a good bet, but “Last chance” and “to go” should be avoided.
  • Features: Email recipients apparently were none too fond of subject lines containing “agenda,” “industry,” “keynote,” and “speakers,” but were more favorable to the term “brochure,” which was about average for opens, but above-average for clicks (9.7%) and CTOs (10.2%).
  • Benefits: “Learn” performed the worst out of this group of terms, while “exclusive” was slightly above-average in each metric. “ROI” scored best, with above-average open (9.3%), click (42.7%) and click-to-open (30.5%) rates.
  • Call to action: B2B event marketers may want to pay more attention to these. “Badge,” “download,” “invitation,” and “registration” all scored above-average in each of the 3 metrics, with “download” overall seeing the best results. (Note that there were discrepancies in the unsubscribe rates of these terms, but those are not taken into account for the purposes of this article.)
  • Free stuff: “Game” was below-average in each of the 3 metrics, while iPad won out in a battle of tablets with Kindle. Subject lines with the term “iPad” were above-average in opens (1.9%), clicks (17.5%) and CTOs (15.2%), while those with the term “Kindle” were below-average in each of those metrics. “Win” was slightly below-average in open rate, but 30+% higher in click and CTO rates.

B2C Events

  • Money: Each of these currency symbols – $, £, and € – performed better than average in open rates, but worse in click and CTO rates. The dollar sign showed the biggest variance, scoring farthest above-average in open (25.5%) rates, but also furthest below-average in click (-74.9%) and CTO (-80%) rates.
  • Ticket sales: The same dynamic mostly applied to these terms also. “2 for 1,” “cheap,” “discount,” “early bird,” “offer,” and “tickets,” were all above-average in open rates, while being below-average in click and CTO rates. “Save” was the worst performer, below-average in each metric.
  • Show features: Once again, the majority of these terms (“exclusive,” “explore,” “program,” and “reasons”) did well getting opens, but were below-average in click and CTO rates. “Preview” and “win” managed to get above-average open and click rates, but fell below the average in click-to-open rates.
  • Urgency: These terms again showed the same pattern: “last chance,” “meet” and “still time” each achieved above-average open rates, but fared far below the average in click and click-to-open rates.
  • Call to action: At the risk of sounding like a broken record, “opens,” “register,” “tickets,” “visit,” and “!” each followed the same dynamic outlined above. “Register” fared the best out of those terms, with the highest open rate (56.6% above average), and click (-0.8%) and CTO (-36.7%) rates closest to the average.
  • Free stuff: “Game” was below-average in each of the 3 metrics, as it was with the B2B event sector, while iPad again won out in the battle of tablets with Kindle.

Retail and E-Commerce

  • Incentives: Retail and e-commerce marketers should avoid including “cheap,” “free,” or “save” in their subject lines, as each of these fared poorly. By contrast “% off” and “sale” both scored above-average in each of the 3 metrics. It was a mixed bag for “half price” and “win,” with the former managing above-average open rates (11.5%) and the latter above-average CTO rates (9.2%).
  • Calls to Action: It was an ugly performance for “buy,” with these emails seeing open rates 19.3% below the average, click rates 59.1% below the average, and click-to-open rates 49.3% below-average. “Order” fared a bit better, getting over the hump with open rates (6.2%), but behind in click (-19.8%) and CTO (-24.5%) rates.
  • Events: As a whole, subject lines containing event terms performed very badly. “Birthday,” “Christmas,” “holiday,” and “summer” each were below-average in opens, clicks, and click-to-opens, and “launch” only avoided that fate by barely crossing the average in open rates (0.3% above-average).
  • Benefits: “Free delivery” was the big winner here, with open (35.9%), click (81.3%) and click-to-open (33.4%) rates all far above the average. “Available” and “new” turned in decent performances, with above-average open and click rates and below-average CTO rates. “Essential” and “offer” did not get the desired responses from consumers, faring below-average in each metric.
  • Superlatives: Recipients did not find subject lines containing superlatives to be particularly engaging. “Fantastic,” “good,” and “exclusive” were below-average in each metric, while “great” (14.7%) and “latest (95.4%) were only able to see above-average rates for opens.

Charities

  • Donations: First the worst performers: “gift,” “give,” “order,” “presents,” and “support” each failed to generate even average open, click, or click-to-open rates. “Donate,” “join” and “member” scored above the average in opens, but were behind in clicks and click-to-open rates. “Volunteer” fared well in open (55.6%) and click (44.9%) rates, while falling off the pace in click-to-opens (-6.9%). It was the same story for “help.”
  • Money: Subject lines containing the £ symbol fared poorly, while those with “% off” hewed close to the average in each of the 3 metrics.
  • Events: “Challenge,” “Christmas,” “event,” “marathon,” and “run” each performed better than average in open rates, but below-average in click and click-to-open rates.
  • Content: This was a mixed bag, although overall most content terms fared poorly. “Action,” “campaign,” “child,” “inspiration,” “lives,” “today,” “video,” “views,” and “win,” all failed in their attempts to generate responses from recipients, falling below the average in open, click, and click-to-open rates. “Difference” had poor click (-70.8%) and click-to-open (-75.3%) rates, but boasted an above-average open rate (18.2%). Of the group, “news,” “society” and “update” performed best, each generating above-average open and click rates. “News” in particular scored well with an open rate 60.7% higher than the average and a click rate 50.7% above-average. Even so, “news,” “society,” and “update” each had below-average click-to-open rates.