To commemorate the 33rd anniversary of the invention of email, Aaron Beach and Victor Amin from our Big Data team revealed the results of a study on global email engagement and email subject line analysis.

With high engagement rates being every sender’s goal, knowing what devices are most popular for interacting with email and what content is resonating most with readers, are two of the best ways to help you get there.

Following is a guest post from Aaron and Victor that shares the results from their study.

Global Email Engagement Study

(The data for this study was collected over two 10-day periods in 2014 and 2015 respectively, with a data set spanning more than 10 billion emails sent.)

  • Apple-manufactured devices retain the crown as the most used platform to access emails. Nearly half of email opens in the US (45%) tracked by SendGrid have been accessed on Mac desktops, Macbooks, iPhones and iPads.
  • Windows-based devices are the second fastest growing segment for email opens globally. On average, emails opened per day on Windows devices in the last year, accounted for a 3.39% increase over the prior year.
  • Android and Linux-based devices are the two fastest growing segments for email opens in the US, growing 71.4% in the last year.
  • Canada is the largest region for email readership, representing 7.9% of email opens in the last year.
  • Australia is third in email readership, with 7.0% of email opens in the last year.

Email Subject Line Analysis

Some of the most frequently asked questions we receive in regards to email content here at SendGrid revolve around email subject line length, copy, and creativity. We’ve previously shared some thoughts on the blog around our suggested best practices, but now we’re turning to our senders’ data to see what the story is.

(The data for this study resulted from analyzing 5 million unique subject headers in nearly 18 million emails.)

  1. Shorten Subject Headers—3 Words Wins Out: While 7 words is the most common subject line word length (14.0% of subject lines), 3 word subject lines (1.6% of subject lines) have the highest engagement rates (21.2%, compared to 17.2% overall and 15.8% for 7 word subject lines).

-Measuring engagement rates by number of character lines tells a similar story: longer subject lines have lower engagement rates. Past 15 characters, each extra character is correlated with a 0.03% absolute decrease in engagement rate (or about 1% per 33 characters).

  1. Choose Your Buzzwords Carefully: Recipients prefer certain words over others.  Subject lines referring to “yesterday” and “tomorrow” have higher engagement rates (20.5% and 22.3%, respectively) than “today” (11.8%).

-Subject lines with “soon” have higher engagement rates (21.9%) versus subject lines referring to “now.

-Email subject lines that use the word “free” have significantly lower engagement rates (13.1% versus 17.2% for subject lines without “free”).

  1. Eliminate Links and Hashtags: Subject lines that contain URLs do poorly, with average engagement rates of 9.9% (compared to 17.2% for subject lines that do not contain a URL). Subject lines with URLs in them are rare (fewer than 0.4% of emails).

-Subject lines that contain #hashtags do poorly, with average engagement rates of 10.5% for subject lines with a single hashtag (compared to 17.2% for subject lines that do not contain a #hashtag). Thankfully, emails with hashtags in them are rare (fewer than 0.2% of emails).

We recommend using this data as a guideline for your email program, and as always, make sure you’re testing into these suggestions. Analyze your own data (through SendGrid’s Event Webhook and Advanced Statistics) to ensure you’re making the most educated decisions for your recipients.

If you’re interested in more email content suggestions, check out our SlideShare: Email Content 101 and to reference more information from the data shared above, read the press release here.



Jillian Wohlfarth
As SendGrid's Director of Content, Jillian is responsible for ensuring that SendGrid provides valuable thought leadership content through the blog, whitepapers, webcasts, and more. When not writing and editing, you can find Jillian frequenting Denver restaurants in search of the best queso.