Email marketing is using email addresses to communicate a message to an audience who have chosen to participate in that messaging with you.
So, a person has chosen to interact with your business and signed up in some way to receive your emails. The emails can be scheduled or planned out but not necessarily. The emails are not specific to the customer interaction at the moment. They are informing your audience of your products and keeping a line of communication open between you and them.
Lead generation is a marketing approach that involves pinpointing consumers who may become customers in the future. It involves leading a potential customer through a process to sell them a specific product or service at the end of this process. The main point with lead generation is to focus on a specific product.
This means you would set up a marketing campaign of 2-3 emails crafted to lead the potential customer through the sales process with the goal being to sell the specific product at the end.
Now, you should not let this specific audience fall into a general email list - they obviously were interested in your book or product/service you were giving away, right?
You send out a follow-up email after your marketing campaign is complete and if they are still interested in the product, they can click on a link to your website or call a number to speak to a representative - you don’t want to lose this audience, you want to lead them to buying the specific product/service.
Ultimately, you need to think about which marketing strategy will work best for your business and your sales goals - utilizing lead generation or email marketing.