DoubleClick recently released its Q1-2005 email metrics report (http://www.doubleclick.com/us/knowledge_central/). Its quarterly reports are often cited as good overviews for the overall state of the email marketing industry. Most of the numbers move in small increments over each quarter, but this quarter's report highlights some clear trends.
First, click-rates were fairly stable, dropping only a few basis points from 8.4% to 7.9%. These rates have remained fairly consistent over the years, ranging from 7.5% to 9.2%. Second, bounce rates have improved over the last quarter, 90.6% to 91.7%. This improving trend has been consistent for three years and most likely reflects the dual impact of improving spam filters (fewer false positives) and increased focus on deliverability by emailers. Third, and most notably, open rates continue their decline, dropping from 32.6% in Q4 to 30.2% in Q1. This drop has been pretty consistent since open rates peaked in 2003. While this last statistic might imply that people are reading less email, the consistent click-rates suggest otherwise. The most likely reason behind the drop is the increased used of image blocking in popular desktop and web email clients. (Opens are tracked by using small, invisible images. Blocking all images means open events can't be measured.)
Overall, the market continues to be in good shape, and some of the positive trends continue to support the efficacy of email as a marketing channel.