Open rates on marketing email and newsletter open rates were 29 percent lower in the fourth quarter of 2005 than in the third quarter, probably due to image blocking by Gmail and Outlook as well as the immense volume of holiday-season emails, writes ClickZ, citing eRoi's "Q4 2005 E-mail Statistics" report, based on data from email campaigns sent by the company. Click-through rates also fell - 21 percent - for the same period.

eRoi found that Friday was the best day for sending email, in terms of open and click-through rates (21.0 and 4.0 percent, respectively), during the fourth quarter. Tuesday had the second-highest open rate (20.8 percent), and Thursday had the second-highest click-through rate (3.7 percent), followed closely by Tuesday (also 3.7 percent).

Email volume is likely correlated to open and click rates: During weekdays, the fewest emails were sent on Friday; the most were sent on Monday, which had the lowest click rate (2.7 percent) for a weekday. Also, the smaller the list, the better the open and click rates.

Prior coverage:

- Email Volume Affects Read and Click Rates, List Size Matters
- Best Day for Emailing Is a Moving Target
- Optimal Day of Week for Emailing Now Tough to Choose
- Email Send Day Studies Prove Self-Influencing