Email newsletters that arrived in consumers' inboxes on Monday had the highest open rates on average last year, according to a recent report from MailerMailer.

The report, which was based on data from 62,000 US newsletter campaigns sent in 2013, found that emails arriving on Monday had a 12% average open rate in the first half of the year and a 12.9% open rate in the second half.

Emails arriving on Tuesday had the second-highest average open rate in the first half of the year, and Friday took the second-place spot in the second half.

The weekends accounted for the lowest open rates in 1H13, with 9.9% on Saturday and 10.3% on Sunday. In the second half of the year, the lowest open rates occurred on Sunday (9.6%) and Thursday (11.5%).

However, though open rates were relatively low on Sundays, clickthrough rates were high. Sunday had the highest average CTR in 1H13 (2.2%) and tied with Tuesday for the second-highest rate in 2H13 (2.1%).

Saturday had the lowest average click rate in 1H13 (1%); Monday and Wednesday tied for the lowest rate in 2H13 (1.7%).

Below, additional key findings from the report.

Time of Day

  • Emails are most likely to be opened earlier in the day, between 8 AM and 12 PM local time.
  • Open rates on a typical day last year started to escalate at 3 AM, peaked around 10 AM (at 6.5%), then declined slowly over the course of the afternoon and evening.

A key thing to note is that these open times do not necessarily correspond to delivery times, since the emails were often opened many hours (or even days) after arriving in consumers' inboxes.

Subject Line Length

  • Emails with short subject lines, between 4 and 15 characters, had the highest average open rate (16.8%), the analysis found.
  • Emails with longer subject lines had lower open rates on average.

About the research: The report was based on data from 62,000 US newsletter campaigns (1.18 billion email messages) sent in 2013.

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Email Newsletter Performance by Time Sent and Subject Line Length

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image of Ayaz Nanji

Ayaz Nanji is a writer, editor, and a content strategist. He is a co-founder of ICW Media and a research writer for MarketingProfs. He has worked for Google/YouTube, the Travel Channel, and the New York Times.

LinkedIn: Ayaz Nanji

Twitter: @ayaznanji