According to the “Email Marketing Metrics Report” by MailerMailer, 12.5% of unique marketing e-mails were opened in the second half of 2008.

The figure is down from the first half of 2008, when 13.2% of messages were opened.

How often e-mails were opened and clicked varied with the industry of the sender—and the size of the list.

Messages delivered to small and medium lists had higher open and click-through rates than messages delivered to lists of 1,000 or more subscribers.

Religious and spiritual organizations had the highest open rates among large lists, followed by telecommunications and travel companies.

Click-through rates for lists of over 1,000 recipients were also highest for religious e-mails, followed by travel, general consumer and retail.

“A smaller list does not directly affect open and click rates, but mailings to smaller lists may be targeted better, contain more relevant content or have more recent subscribers,” wrote the authors of the report.