Listmonk

Listmonk is an open-source email marketing platform you deploy on your own server. It includes a drag-and-drop editor, advanced SQL-based segmentation for precise targeting, and support for multiple SMTP providers or your own mail infrastructure.

Ideal for organizations that want full data control and don't want to pay per subscriber. If Mailchimp's pricing scales too high as your list grows, Listmonk's one-time setup cost and hosting fees provide a completely different economics model.