The Sendy Ruby SDK by Richard Lee allows to interact with the API to implement newsletters into web projects. With the kit, developers can subscribe, unsubscribe, check subscription status, and create campaign.
Message Bus is a cloud-native application service for email and mobile messaging. The selling point is the high deliverability rate, its ability to scale according to demand and the fact that it's simple enough to be used by developers with limited time and resources. The Message Bus API makes it possible for developers to easily add messaging functionality to their websites and apps.