Top SMTP GitHub Repositories & Tools (2026)

Built from the ground up for speed. Flectar Mail delivers native performance, instant startup, and as little as 20 MB of RAM.

Self-hosted mail server for your own domain: SMTP/IMAP/POP3, CardDAV/CalDAV, React webmail and admin console, one-command Docker Compose.

Cypht: Lightweight Open Source webmail aggregator [PHP, JS]. Supports IMAP/SMTP, JMAP and EWS (Exchange Web Services)

A cross-platform .NET library for IMAP, POP3, and SMTP.

:mailbox: SMTP Server + Web Interface for viewing and testing emails during development.

An OOB interaction gathering server and client library

Emails at the heart of your business logic!

💌 Mail app for Nextcloud

✉️ Open-Source Email API for Developers. Cloud & Self-hosted Alternative to SES, Mailgun, SendGrid.

Official master for the Greenmail project

A PHP library for performing email addresses validation via SMTP

Terminal-based email client for Linux and macOS

qpsmtpd is a flexible smtpd daemon written in Perl

DavMail POP/IMAP/SMTP/CalDAV/CardDAV/LDAP Exchange and Office 365 Gateway - Synced with main subversion repository at