1. Advertising : The best way for someone to know about your email platform is by getting them to know about it. This is where advertisement comes in. Please understand that while it is good, you have to place it where it will be considered. A newsletter that concerns food may gain more consideration on a travel magazine than on a fashion magazine. Place your ads wisely
2. Website: If what I'm assuming is correct, you are probably looking for more market for a product or service, or you are looking for people to subscribe to a newsletter. In this situation, it will be good to get a website as most people are used to doing this online and a website is your footprint in the beloved sands called the internet. Getting a website will make it easier for your potential customers to reach you.
3. Social Media : The social media is a place where information, whether rumor of true, is passed. Getting your self or your product a social media network will be good of spreading information of such so as make them subscribe to your email list. I myself have heard of some products I use thanks to the rumor mill called The Social Media
You can contact me if you wish to discuss more.