Listmonk

Listmonk is the self-hosted answer to Mailchimp: one Go binary plus Postgres that handles subscribers, campaigns, templates, analytics and transactional mail. Point it at any SMTP provider (Amazon SES, Postmark, your own relay) and you own the list. AGPL, every feature included, no paid tier and no hosted version from the maintainer.

Setup is a Docker Compose file, and it barely sips resources: the project cites a 7-million-email campaign peaking at 57 MB of RAM. The parts vendors charge for are just there: OIDC single sign-on, granular roles, scoped API tokens, multi-SMTP queues, and a drag-and-drop builder next to WYSIWYG, Markdown and raw HTML editors. Segmentation is SQL expressions, a gift or a wall depending on you. Solo operators and small teams should stop shopping. Mautic is the move only if you need full marketing automation.

The catch: deliverability is your job. SPF, DKIM, DMARC, domain warm-up and bounce rates are all on you, and one careless campaign can burn a sender reputation. Patch, too: 2026 fixes covered a stored XSS and a SQL injection that let lower-privileged staff reach admin password hashes and SMTP credentials. Kit is free to 10,000 subscribers, so below that you're buying control, not savings.