MarketingVox quotes eROI report, saying that the best day for e-mail is Wednesday. The average open rate on Wednesdays was 25.4% with an average click-through rate of 3.9%. The second-best day to e-mail is Monday, with an average open rate of 24.7% and a 3.1% click-through. Saturday commanded the highest CTR of 5%, but the lowest open rate with 18.7%.