* [Delta Chat Desktop v2.59.1](https://github.com/deltachat/deltachat-desktop) – Desktop application for secure messaging based on email protocols.

* [Go smtpd v2 v2.4.0](https://github.com/chrj/smtpd) – Go SMTP server library implementing an SMTP server with TLS, authentication, streaming envelopes, structured logging, and composable per-phase middleware.

* [smtp-server v3.19.4](https://github.com/nodemailer/smtp-server) – Node.js module for creating SMTP and LMTP server instances dynamically.