According to some research presented by BitBriefs, the number one reason that people who have opted in to your email list turn around and opt back out is irrelevant content.
It's the answer to every client's question--why are my email subscribers going away or, worse, marking me as spam?--and it's backed by the numbers: content is still king.
When people get your emails, they want something of value. If you are a real estate seller, try giving valuable information about the market, top tips for buying real estate or information about your real estate offering (something they haven't seen before). If you're an economic developer, your readers want local news, updates on development and information about the place you represent. If you are in retail, keep it short and sweet when you're presenting a product and give them the information that they crave.
Otherwise, off they'll go.