If you look hard enough you will find research on almost any given topic. For instance, were you aware that there are certain times when sending email marketing is probably a bad idea? There are also times when sending marketing emails makes perfect sense.
Monday and Friday These two days are not as useful to email marketing as other days of the workweek. The primary reason is Monday is generally a time to get back into the swing of work, while Friday is a time to gear down. Your email is likely to be lost in the shuffle. Since most email marketing can be sent out on command this is something to consider when developing an email marketing campaign.
Saturday and Sunday The weekend is generally throwaway days for email marketing for much the same reason as Monday and Friday. If someone is in the office on the weekend, the last thing they are interested in is marketing emails. If your email comes in over the weekend chances are pretty good your email marketing campaign will be subject to a readily used email purge without serious consideration.
It should be noted that you might find some receptivity to email marketing campaigns that are sent out to...