Mailtrain

Mailtrain is the self-hosted Mailchimp alternative that tried to do everything — multi-user support, automation workflows, WYSIWYG templates, advanced segmentation, and detailed deliverability analytics. Built on Node.js and MySQL, it's the most feature-rich open-source email marketing tool if you need structured campaigns with multiple collaborators.

If you need automation workflows, A/B testing, and multi-user collaboration in a self-hosted newsletter platform, Mailtrain has more built-in features than Listmonk. Listmonk is faster, lighter, and easier to deploy but lacks automation. Plunk is the newer alternative with marketing plus transactional in one. Mautic is the open-source marketing automation suite if you need even more.

The catch: Mailtrain is labeled "beta-grade software" by its own developers. The project's maintenance cadence is slow — version 2 was a complete rewrite that broke backward compatibility, and updates are infrequent. Setup is complex compared to Listmonk's single binary. For most indie hackers, Listmonk's simplicity and active development make it the safer bet.