People tend to think of evaluation as something you do at the end of a campaign. In fairness, doing a full evaluation at the end is a massively important part of any campaign strategy. But it’s also helpful to evaluate as you're going along. Lots of brands make the mistake of closing their ears to ongoing issues and save any feedback for the end of campaign evaluation.
When it comes to deciding how to craft that perfect subject line, there appears to be really only one area to avoid: the subject line of 60 to 70 characters. Marketers refer to this as the “dead zone” of subject length. According to research by Adestra, which tracked over 900 million emails for its report, there is no increase in either open rate or clickthroughs at this 60-to-70 character length of subject line.