Everyone is not your customer. And while some people might become customers sometime in the future, there are some people who never will. Make the best use of your marketing efforts by narrowing down to a niche.
Then, even after you have narrowed your market and created a well defined target audience, your customers are not all the same. Some are casual buyers and others are rabid fans. There are some only care about your sales and promotions, while others will be frequent buyers, regardless of the price.
As you start thinking about your customers as individuals, it's much easier to understand what appeals to one and may not interest the other. When you plan your next email newsletter campaigns don't treat your entire list as if there were all the same. If you do, some customers are going to get too much information, while others may not get enough, or get information at absolutely the wrong time.
Create better marketing by dividing and dividing and dividing your email list into smaller and smaller groups. Yes, it does take a little longer to deliver the campaigns, but the results are worth it.