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.
Whether you're seeking B2B or B2C LEAD GEN, you can lease these lists to pump up your email mailing list. You can also harvest email leads through speaking engagements where you can expound on your area of expertise or product value.
One additional comment: for your website make sure and install a roadblock/pop-up to encourage folks to give you their email address when they first visit the website. Other optimization strategies for your website really depend on what type of site you have (ecommerce, general marketing etc.) For example, if ecommerce use tools to get people to give you their email address on the product details pages (i.e. a favorite or share via email to a friend option) since most ecommerce sites see over 40% of their traffic sources and come in on their product pages. For general marketing sites you can consider things like using email sign-up as a roadblock for downloading some sort of white paper etc.
There are endless strategies, tools, and tactics you can leverage here. I personally would start with any low hanging fruit possible. Not knowing your business or having any context makes it more difficult.
I personally love Optinmonster. You can create a series of popups that can be positioned around your website to optimize and encourage people to optin. Focus on the pages with the highest traffic first. I would avoid instant pop-ups as these are just annoying so use delayed popups to ensure the "prospect" is interested. As well exit intent pop-ups are great as well.
Next, I would focus on your copy throughout the website while leveraging A/B testing to see how you can improve your optin copy.
Once those are optimized then I would focus on two areas.
1. Retargeting Ads
2. JV partnerships
3. Guest Posting
4. Paid Media
More than happy to review this with you and share these ideas in greater depth if you're interested.
I worked in digital marketing agencies and this is a usual ask of clients.
There are a few questions that you need to ask prior to this.
1. Who is your target segment (s) and where do they play / live
2. What outcome do you want from engaging with persons from this list
3. If it is B2B, are there professional bodies you can partner with
4. How qualified does this list need to be / How do you intend to qualify the list
Let's talk more for me understand where you are coming for so that we can talk strategy that makes sense for you.