Best Open-source Mail Servers & Relays tools

Haraka

High-performance Node.js SMTP server with modular plugin architecture

Tuta

Secure email with seamless end-to-end encryption across devices

Mailu

Fully featured Docker‑based mail server that's simple to deploy

Plunk

Self-hosted email platform powered by AWS SES

Maddy

Composable all-in-one mail server replacing multiple daemons

Zero

Self-hosted AI-enhanced email client with unified inbox

Mail-in-a-Box

One-click, self-hosted email server that just works

useSend

Self‑hosted email platform delivering reliable, low‑cost SES mail

Go-Guerrilla

Lightweight SMTP server for high-volume email reception in Go