Email open and click-through rates declined sharply in 2009, especially in the latter half of the year, with performance levels varying dramatically by industry and email list size, according to a study by MailerMailer, which also found that open and click rates tended to be highest on Sundays.

The average overall unique open rate*at the end of 2009 was 11.2%, down 10% from a year earlier.

Image blocking, the increased use of email handheld devices, and list fatigue were among the key reasons cited for declining open rates.

Some key findings:

• Subject Lines: Email messages with subject lines of 35 characters or less outperformed emails with longer subject lines, generating open rates 52% higher and click rates 69% higher, on average.
• Bounces increased by 8% over the previous year, but still account for just 1.4% of all email messages sent.
• Bounces by mailing frequency: Marketers sending email less than once a month garnered bounce rates more than 200 times that of those sending monthly.
• Personalization used in messages, but not necessarily in subject lines, continued to perform well, generating open rates 7% higher and click rates 80% higher, on average, than email messages without personalization.

Below, additional findings from the July 2010 edition of the Email Marketing Metrics Report, including the best day to send email and open and click rates by industry and list size.

Best Day to Send Email: Sunday

Emails sent on Sundays during the first half and second half of 2009 registered the highest average open rates, 14.1% and 12.2%, respectively.

Messages sent on Sundays registered similarly higher click rates in the first half and second half of 2009, 4.1% and 2.6%, respectively.

Open Rates by Industry

Email open rates varied widely by industry, with some sectors' open rates at 20% or more and others' at 10% or less.

Open rates across the top-performing sectors in 2009 were as follows:

• Agriculture: 25.3%
• Religious: 21.0%
• Transportation: 18.1%
• Non-Profit: 17.3%

The industries with the lowest open rates were the following:

• Entertainment: 9.2%
• Banking: 8.2%
• Marketing: 7.4%
• Medical: 7.3%

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Open Rates by List Size

Smaller lists tend to perform better, and that trend continued in 2009: Smaller lists (fewer than 499 email addresses) garnered higher open rates than medium-sized lists (17.8%) or large (1,000+ email addresses) lists (14.3%).

Small lists registered open rates almost as high as 40% in some sectors:

• Agricultural: 39.8%
• Religious: 36.0%

Medium-sized lists had higher open rates than small or large lists in two sectors:

• Wholesale: 25.6%
• Media: 25.3%

In some segments, large lists did produce open rates higher than 20.0%:

• Agricultural: 24.9%
• Religious: 20.5%

Regarding email stabilization, roughly 30% of the total opens occurred two hours after email delivery; 75% of total opens occurred after 23 hours of email delivery.

Click Rates

The average overall unique click rate** at the end of 2009 was 1.6%, down 42.9% from a year earlier.

Similarly, list fatigue was cited as a key reason for declining click rates—as was "links that are not live." In an attempt to thwart phishing schemes, many email clients (e.g., Outlook, Yahoo) deliver messages without making the links clickable. The recipient must take an action to enable those links.

Click rates also varied widely by industry, with some sectors' click rates at 9% or more and others' at 1% or less. The top-performing industries in 2009 were the following:

• Religious: 10.5%
• Transportation: 7.6%
• Environmental : 4.8%
• Retail: 4.5%

The industries with the lowest click rates were the following:

• Legal: 0.9%
• Marketing: 0.8%
• Entertainment: 0.7%
• Restaurant: 0.7%

Click rates also varied by list size: Smaller lists (fewer than 499 email addresses) garnered higher click rates (5.4%) than medium-sized (3.1%) and large (3.1%) lists.

The number of links embedded in a message also affected click rates: Email messages with 20+ links outperformed messages with fewer links, generating a click rate of 2.9%.

*Open rate is calculated by dividing the number of email messages opened by the total number of email messages sent.

**Click rates are calculated by dividing the total number of unique clicks by the product of the number of links in each message and the number of total recipients.

About the data: The data for this report is based on the study of 900 million email messages sent by MailerMailer customers from Jan. 1 to Dec. 31, 2009, to a minimum of 25 recipients.