Mox is a modern full-featured open source secure mail server for low-maintenance self-hosted email. Quick and easy to start/maintain mail server, for your own domain(s). SMTP (with extensions) for receiving, submitting and delivering email. IMAP4 (with extensions) for giving email clients access to email. Webmail for reading/sending email from the browser. SPF/DKIM/DMARC for authenticating messages/delivery. Reputation tracking, learning (per user) host-, domain- and sender address-based reputation from (Non-)Junk email classification. Bayesian spam filtering that learns (per user) from (Non-)Junk email. Rejected emails are stored in a mailbox called Rejects for a short period, helping with misclassified legitimate synchronous signup/login/transactional emails. Automatic TLS with ACME, for use with Let's Encrypt and other CA's. DANE and MTA-STS for inbound and outbound delivery over SMTP with STARTTLS, including REQUIRETLS and with incoming/outgoing TLSRPT reporting. Web admin interface that helps you set up your domains and accounts (instructions to create DNS records, configure SPF/DKIM/DMARC/TLSRPT/MTA-STS), for status information, managing accounts/domains, and modifying the configuration file. Account autodiscovery (with SRV records, Microsoft-style, Thunderbird-style, and Apple device management profiles) for easy account setup (though client support is limited). "mox localserve" subcommand for running mox locally for email-related testing/developing, including pedantic mode. Most non-server Go packages mox consists of are written to be reusable.

At least it tells you how to compile and install it so you don't have to reverse engineer a bunch of Dockerfiles.

chasquid is an SMTP (email) server with a focus on simplicity, security, and ease of operation.

It sends and receives email as a typical MTA (for example, can be used instead of Postfix or Exim), and it is designed mainly for individuals and small groups.

It's written in Go, and is open source under the Apache license 2.0.