Marketers online are not as effective if they do not have a list of email addresses they market to. A website alone is not enough. People forget easily. Once your site has been visited and does not interest the person at the moment, chances are, that person will never get back. That is, unless you were able to offer to be subscribed to your newsletter or update. A simple email address with the first name will do. When you have gotten that, you can then write a letter (or get a saved letter), address it to the first name that has been supplied and send it to the email address. Follow up letters are also usual. That way, the interest may perk up later. That is the usual way to build your email list. It is slow, it depends on the people who went to your website, but you have a higher percentage that those people are interested, more likely.
If you are depending on and believe on the numbers game principle then you can, instead, buy email marketing lists who are already interested in particular niches such as yours. Since the percentage of response rate is smaller than the above procedure, with a huge number in your list you can still end up with a lot of responses. You pay, but you started right away, fast.