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dkim

hMailServer: a free, open-source mail server for Windows and Linux. SMTP, IMAP and POP3, webmail, a REST API, the Control Panel and the browser Control Deck. AGPL-3.0-or-later. Maintained by Progressive Robot Ltd.

Custom-domain email done properly: alias domains, SPF, DKIM and DMARC, Gmail filters, accessible signatures and Outlook templates you can build from code.

CI/CD component: send your real email template through your SMTP relay and fail the pipeline when SPF, DKIM or DMARC breaks or the spam score drops

Declarative, idempotent mail server configuration script

DMARC library and milter module implemented in Python.

Full email server solution with docker