Studies connecting email subject lines to engagement rates is scarce. Even in the limited studies done, the use of the subject line is not addressed in detail. And, most of these studies are being done in either user forum scenarios or academic settings. As we all know, results obtained from theoretical studies can be totally different from practice. All in all, there is a lack of credible academic research on the link between subject line and response rates. So, the email response rate depends from one company to another. What works for a company may not necessarily work for another.