We would like to simplify our email newsletter process and convert to some form of RSS to newsletter. We have opt-in subscribers on a major newsletter provider who does not offer this option, otherwise we would be happy to continue with them.
I know Aweber does offer RSS to newsletter, however not with a simple way to upload existing subscribers.
I assume you're generating your RSS through some sort of CMS involving a database. Why not simply have the database export the same information in the format that your current newsletter provider supports?
It sounds like you're already using a 3rd party company for your newsletter. I was just suggesting you format your data to meet their system. It would be the same as outputting an RSS feed for the most-part.