Mailtrain GitHub - Mailtrain-org/mailtrain: Self hosted newsletter app is a mailing list manager built in Node with some basic API functionality.
I would be very pleased to be able to subscribe users to lists, unsubscribe, send out one off campaigns to singular/list members, or trigger a mailout of an existing list featuring content from an RSS feed.
I could provide a base install of Mailtrain 2 for testing.