Best open-source email stack

Outbound and inbound delivery server.

Full self-hosted mail and groupware suite with a strong admin UI.

Compact all-in-one SMTP, MX, IMAP, and authentication stack.

Newsletter manager and broadcast.

Notification orchestration across channels.

Transactional email dashboard with SMTP, bounce handling, and analytics.

Local capture for dev and staging.

Templates as React components.

Vendor-neutral template language.

Responsive email framework with Inky, Sass, templates, and inlining.

Simple MIT-licensed template layer used across many email renderers.

Safe user-editable template language with strong commerce adoption.