Monday was once considered the best day for sending out commercial email - but that's no longer so, according to a new report, eMarketer writes. Instead, ExactTarget asserts, the "best day" for sending out commercial emails is still a moving target, though the second half of the week is likely better than the first.

But the "best days for opens are not necessarily the best for clicks," says ExactTarget: Maximizing open rates is important for brand exposure, but generating clicks is important for conversion.

Starting in July 2004, the best days for maximizing open rates shifted to later in the workweek, with less than 0.5 percent difference among Wednesday through Friday. However, Sunday and Saturday yielded the highest click-through rates.

According to ExactTarget, over 97 percent of email campaigns are sent on weekdays, and Wednesday is the peak day, accounting for 22.4 percent, ahead of Tuesday with 21.4 percent.