If you are considering testing to find the best day of the week to send your email, the Email Diva has some advice for you: don't bother. Or, perhaps, make this the LAST thing you test, after you have optimized your user experience, opt-in page, format, creative, copy, links, subject line and offer.
Judging by the number of articles on this subject, many marketers feel that if they can just find that holy grail -- the best day to mail -- it will magically improve their programs. Unfortunately, judging by the number of conflicting reports, there is no such thing as a best day. You will find experts confidently reporting that, based on their experience, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday and/or Saturday is the best day to send email.
Early in my email career, I tested this as well, and each retest yielded a different answer than the previous test. One thing that was far more useful was to graphically chart response over time. We found that there was an uptick on Mondays, regardless of the day the email was sent. This led us to theorize that many of our subscribers were reading our non-business content at work, as a diversion, which helped direct our content. Rather than trying to find the magic best day, chart your responses to see whether you can use the data to learn something about your audience.
Even if there were one universal best day to send email, it wouldn't make sense to send your email the same day as everyone else. In the world of direct mail, a truism was that January was a bad month to mail, being just after the holidays, etc. We had great success with January mailings, precisely because of this thinking. We didn't have much competition in our customers' mailboxes.
What you're trying to find is that magic moment when your customer is online with spare time and mental bandwidth. Think of your own experience. Can you tell me that there is a specific day or time of day when you predictably reach this marketer's nirvana, week after week? Of course not. You may be bored on the weekend and do work-related browsing, or take a break at work for some well-deserved shopping.
This is not to say that you shouldn't consider your audience and site characteristics and send on the day that makes sense for these factors. But if you have developed an email program that delivers exceptional value, your consumers will set aside your email and read it when they find the time. That's why your focus should be on providing value, not searching for this magic best day. Efforts to build a better program will yield far better results than trying to hit a moving target.
The Email Diva