You can send your already-written posts as a newsletter to the public, create a new post from the start, and send it as a newsletter. This can be simply done on the Newsletter tab in the right-hand sidebar. You just need to follow the instructions:
On Newsletter Tab, enable the option “Send Post as a Newsletter”
Send Newsletter on Publish or Schedule a Campaign
Important: if you decide to schedule your newsletter, you will also be asked to schedule the time to send your newsletter.
Select your destination list, destination group, and your template
Add your subject line
Send your Newsletter
Once you have finished adding the details of your Newsletter, you can click the Update & Resend Newsletter button. This will update your post and, if it was already published, without being sent as a Newsletter, it will become a Newsletter for the chosen audience.
Important: If you are creating a new post that has yet to be published and you plan to send it as a newsletter, the Update & Resend Newsletter button will not be present.