As a growing business, you may also be looking for a CRM solution, and you'll find that the more advanced email marketing services have begun to crossover into CRM. It makes sense: Both types of software deal with managing and communicating with customers. A handful of these services are one-stop shops, either offering both email marketing and CRM out of the box or as add-on services.
Take the email below from Paperless Post, for example. I love the header of this email: It provides a clear CTA that includes a sense of urgency. Then, the subheader asks a question that forces recipients to think to themselves, "Wait, when is Mother's Day again? Did I buy Mom a card?" Below this copy, the simple grid design is both easy to scan and quite visually appealing. Each card picture is a CTA in and of itself -- click on any one of them, and you'll be taken to a purchase page.
Watch the growth of your list. Is your email list growing or shrinking? If more people are unsubscribing than are registering to your list, it's a good sign that you need an entire strategic overhaul on your email policies. If there are a lot of people unsubscribing it could be because your content is not relevant to the people that you're sending it to. In this case, try to segment your list differently or change the type of content that's being delivered through your email blasts.
Sample review: Optinmonster “has various forms you can embed on your site to help with email conversion but one of the most interesting ones is the popup. You can set the popup only to appear on ‘exit intent’. This means that your website visitor can browse all they want and when they are about to exit the website you can have a popup appearing tempting the visitor to leave their email address.” — RazorSocial (World)