phpList

phpList is a long-standing open-source email marketing platform that's been running since 2000. It supports subscriber segmentation, automation workflows to trigger campaigns based on behavior, and detailed analytics to measure campaign performance. You can self-host it or use managed hosting from phpList's partners, and the large user community (75,000+) means abundant plugins, templates, and forum support.

It fits organizations that need reliable email infrastructure without being locked into a SaaS vendor. Compared to modern platforms, phpList requires more technical setup but offers deeper customization and substantially lower costs once deployed. It's particularly popular with nonprofits, agencies, and publishers sending email at scale who can't justify climbing monthly subscription fees.