Short answer: It depends.
That's according to a report from eMarketer called Picking the Best Day To Send E-Mails. (This report is available only until December 11, 2005; after that it's only available to subscribers to eMarketer's eStat Database -- which costs $5,000 for a one-year subscription.)
Overall, Sunday is the best day for open rate (30.8%) and click rate (7.2%), with Friday second best and Wednesday the worst (with an open rate of 22.8% and a click rate of 3.5%).
But there are significant differences depending on list size:
- Lists under 5,000: The best days are Saturday and Sunday
- Lists 5,000 to 24,999: Friday is best.
- Lists 25,000 to 99,999: Monday and Friday.
- Lists 100,000 and above: Monday through Wednesday.
Smaller lists tend to do better, probably because they are more tightly defined and thus more relevant. That tells you if you have a large list, segment it.
Email fundraising is still tiny compared to the postal variety. But it's growing. And we have a lot to learn.