* [Haraka v3.2.0](https://github.com/haraka/Haraka) – Highly scalable email server with a modular plugin architecture.

* [DKIM Verifier v6.3.0](https://github.com/lieser/dkim_verifier) – Thunderbird add-on that verifies DKIM signatures per RFC 6376.

* [Maddy Mail Server v0.9.5](https://github.com/foxcpp/maddy) – Composable all-in-one mail server implementing SMTP (MTA/MX), IMAP storage, and security protocols such as DKIM, SPF, DMARC, and DANE.