Emails from brands with special offers in their subject lines tend to underperform those without special offers in their subject lines, according to recent research from Yes Lifestyle Marketing.

The report was based on data from nearly 8 billion emails sent in 4Q16 by brands in a range of industries.

The researchers examined how email subject line performance is affected by six types of offers: Buy one, get X; percent off; dollar amount off; free shipping; free gift; and loyalty incentives (e.g., "Member Exclusive: 10% off").

Some 30% of all email campaigns examined included specific offers in their subject lines; 44% of campaigns sent by retailers included specific offers in their subject lines.

Across all industries, emails without explicit offers in their subject lines have 28% higher open rates than those that include offers. Click and CTO rates are 67% and 34% higher, respectively, for messages without explicit incentives in their subject lines.

The exception is email subject lines that include loyalty incentive offers, which have a 9% higher open rate, 20% higher click rate, and 12% higher CTO rate than emails with subject lines without offers.

The performance of specific offers in email campaigns sent by retail brands is more mixed than performance across all industries.

Retail emails without specific offers in their subject lines have higher open and click rates than those that include offers. However, loyalty incentive offers lead to a higher CTO rate, and all of the other offer types lead to higher conversion rates.

Email subject lines that include the word "deal" but do not include a specific offer tend to outperform those that include a specific offer, the analysis found.

About the research: The report was based on data from nearly 8 billion emails sent in 4Q16 by brands in a range of industries.