Research has shown that the subject line of an email is vitally important and plays a huge role in terms of the success of the marketing campaign. If the subject line is not appealing then people will not bother to open or read the email.
Many businesses still use email marketing as part of their online marketing strategy and it can work very well. Although it can be tempting at times, never buy in a list of email addresses to use as not only can the data be illegally obtained but your success rates are bound to be low. Emailing to your own existing database is often likely to get you a better response. Lots of companies that allow you to send mass emails through their servers stipulate that you can only use a list of opted in email addresses and not ones that you have obtained elsewhere.
The subject line is of massive importance on an email as it is often the first thing the viewer will read and can be the deciding factor between opening the email and deleting it. Try to do your research and trail different subjects to see which ones get the best open rate.