You can think of Mautic as an open source alternative to proprietary services like MailChimp, Campaign Monitor, or Constant Contact on steroids. It allows newsletters (with embeddable sign-up forms for your website), plus far more complex rule-based automated email campaign solutions.
The OER Foundation is working with an open source tool called Mautic - there's a hosted service (the "reference instance" provided and supported by the Mautic company) for which you pay a monthly fee based on the number of "contacts" you have... or, you can host the same service yourself, on your own infrastructure.
We originally used the "Mautic Cloud" hosted service, but for reasons known only to them, they decided to jack up prices on their existing customers - in our case, about 10 times. Not a good way to keep your customers happy. But, thankfully, Mautic is open source. That means we can take control of our own destiny. We have now got OERu Mautic and it's based on our own package of the Mautic system (which is made up of quite a few components that all have to fit together properly for the system to work).
If you want to see how we did it - and perhaps implement the same solution for your own institution/organisation, we've written a comprehensive how-to! Get in amongst it, and let us know how you go!