Email (9)

• Postfix - ArchWiki (wiki.archlinux.org) tutorial
  setting up Postfix on Arch: main.cf and master.cf, aliases, local vs virtual user delivery
  Arch Linux Mail Server #
• Home | Dovecot CE (doc.dovecot.org) reference
  IMAP, POP3, LMTP and ManageSieve server docs for the open-source Community Edition; Pro is commercial
  Commercial Support Mail Server #
• OpenSMTPD (opensmtpd.org) tool
  OpenBSD's server-side SMTP implementation of RFC 5321, small and auditable, ISC licensed
  BSD Mail Server #
• Rspamd — Email Security System (rspamd.com) tool
  Async C spam and phishing filter: regex rules, RBLs, greylisting, SPF/DKIM/DMARC/ARC, ML scoring
  Mail Server Spam Filtering #
• OpenDKIM (opendkim.org) tool
  C library plus milter giving sendmail-compatible MTAs DKIM signing and verification, also VBR and ATPS
  Mail Server Spam Filtering #
• dmarc.org – Domain Message Authentication Reporting & Conformance (dmarc.org) reference
  DMARC email authentication and reporting over SPF/DKIM; policy, alignment, RFC 9989-9991 standards track
  DNS Spam Filtering #
• Thunderbird — Free Your Inbox. (Thunderbird) tool
  Donation-funded desktop client unifying mail, calendar, contacts and chat; no ads or data collection
  Privacy #
• The GNU Privacy Guard (gnupg.org) tool
  command-line OpenPGP implementation with key management, S/MIME and ssh support; Gpg4win for Windows
  Command Line Encryption #
• ClamAVNet (clamav.net) tool
  Signature-based malware scanner with daemon, CLI tools and auto-updating definitions; mail-gateway staple
  Security Hardening Vulnerability #