Your current customer base is a great place to start building your email list. If you have a CRM system, you probably have already have clients’ email addresses. The more information you have, the better. Start with an overarching list that includes all customers and then keep segmenting and branching out based on who your customers are, where they are located, what they purchased, or any other number of relevant variables that you have collected. If you don’t have a CRM and have not been collecting emails of past clients, then you’ll have little tougher time. Try calling your past and current customers, look on their website for contact information or reach out on social media to acquire their emails. Starting with your current and past customers will give you a solid foundation to build on.
In this context, I guess each post can’t be thought of in isolation, but in terms of a mini content ecosystem that comprises of a great blog post optimised for on-page SEO, an upgrade to that post tailored for that specific content, various on-page email conversion points including an exit pop-up or similar -and then you combine all this with your off page link building and outreach efforts. That could be over 5,000 words of content all in just that one package.