Have you thought about how many different reasons there could be for that?
Here is the first reason I want you to look at - Your Subject Line. Before anyone can even see what you've got in that newsletter, all they're going to see is your brand with the subject line right beside it. And if that subject line doesn't captivate their attention, doesn't engage them in a certain way or doesn't intrigue them, what they're going to do is click DELETE and go on to the 100 other emails in their inbox.
More and more people are getting more and more emails every day and this means you need to work harder to make sure that subject line is going to really get someone's attention when they see it in the inbox among the hundreds of other emails waiting to be opened.
Need ideas on a great subject line? Put together a focus group of people similar to your target market. Test different subject lines in front of different people, or at the very least use a split-test the next time you run a campaign.
Split-testing is when you divide a campaign into segments, and make one change to each segment to see how it performs compared to the others. For example, if you have a list of 300 people in your email list, make 3 lists of 100, and send each segment an email with identical content, but with different subject lines to see which one gets a better open-rate.