listmonk

An open source newsletter and mailing list manager that also sends transactional email, packaged as a single Go binary with a web interface for subscribers, templates and campaigns. Subscribers can be segmented with SQL queries into dynamic lists, campaigns support a visual template editor, double opt-in and unsubscribe handling, and a REST API drives everything from outside.

Small teams and community projects use it for product announcements, weekly digests and password reset messages without handing their mailing list to a hosted provider.

Running it on your own server means the subscriber list stays on your hardware, the sending path is yours to choose, and there is no per-contact pricing as the audience grows.