* [Delta Chat Desktop v2.43.0](https://github.com/deltachat/deltachat-desktop) – Desktop application for secure messaging based on email protocols.

* [Haraka v3.1.3](https://github.com/haraka/Haraka) – Highly scalable email server with a modular plugin architecture.

* [smtpmock v2.5.2](https://github.com/mocktools/go-smtp-mock) – Go-based configurable multithreaded SMTP mock server for testing, supporting RFC 2821/5321 and customizable command behavior.