Email Marketing is a very powerful way to promote your opportunity. The problem is, it takes a big list to see any real results. Many marketers do not how to build a list in the first place.

The first thing you need to do is create a squeeze page or landing page that will spark interest. Give something away for free, this always works. Be sure to include an opt in form that asks your visitors for their name and email address.

Once you have that created, then you can go to places such as forums, social networks, twitter and blogs to create interest. Do not spam these places, simply interact and have your signature or profiles have your squeeze page URL in it. When people get to know you and you build trust, they will begin to click on your link and opt in. Also, traffic exchanges work well with squeeze pages. Get creative and be consistent and you will begin to see your list grow.
And never limit your options for the type of social networks or blogs that you sign on to for the purpose of creating interest. Because even if your product is a very specific one, you are not going to get as much traffic on a forum about Caravan insurance as you are on a forum about 30 Rock. So even though there will be less hits per person to see your link on the non specific website, there will be a lot more traffic which means that there will be many more potential links.
No matter what you do just be creative and remember never to rule anything out until you try it!