A useful footer. Below your main content is the footer of your email. It should contain a clear and simple way for your reader to unsubscribe, as required by the CAN-SPAM Act. Mention why they are getting the email (they signed up), and how to contact you. Email apps often take care of this for you, but just be sure it is included. The footer area is where you could do “self-advertising” if you wanted to. Keep it simple, if you choose to do it, preferably just one or two “ads” or links.
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.