Marketing e-mails sent on Sunday generate 7.2% click-through rates

eROI said that email read and click rates are the lowest during the middle of the week and the highest on Sunday and Friday. Micromailers, with less than 5,000 recipients, tend to perform similarly. Read rates in excess of 35% and click rates between 5% and 9%. With smaller prospect lists they allocate more time on creative and marketing plan dollars per prospect. Small senders, between 5,000 and 24,999 readers, start to see dramatic fluctuations in behavior and middle of the week mailings. Tuesday through Thursday become the prominent times email are sent compared to smaller senders. Mid-size senders, with 25,000-99,999 recipients, notice wide swings in read and click behavior with Monday and Friday registering the highest percentage of reads and clicks. On Friday, reads register a 60% increase over the average for the week, and clicks post a staggering 169% premium over the average for this size mailer.

Q3 2005 e-mail delivery and click rates
  Sent Read Click
Sunday 954,570 30.8% 7.2%
Monday 10,501,562 25.6% 3.9%
Tuesday 15,414,657 23.9% 3.9%
Wednesday 16,257,590 22.8% 3.5%
Thursday 15,725,986 23.1% 3.7%
Friday 11,105,552 27.0% 5.3%
Saturday 918,268 23.7% 3.9%
Source: eROI