Sometimes you want to send out a blog post and a newsletter, but want some content to just be in the email, not your site. This includes things like salutations, promotions, and disclaimers. You can use email-only headers and footers for these.
Start writing a post. Click on the menu dropdown in the top right. You'll see the ability to add email-only headers and footers.
You can type in whatever you want in the header or footer and hit Insert once you're done.
You'll see a chip telling you if an email-only header or footer is inserted in your post.
The final blog post on your site will not contain the content in the email-only header and footer. The email newsletter will contain both if set.