Top 2 spamassassin open source projects

Production-ready fullstack but simple mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.) running inside a container.

Hermes Secure Email Gateway is a Free Open Source Ubuntu 18.04 or 20.04 Server based Email Gateway that provides Spam, Virus and Malware protection, full in-transit and at-rest email encryption as well as email archiving. It features the latest email authentication techniques such as SPF, DKIM and DMARC.