Summary

Adds a reusable email server stack for managing client email domains, based on Docker Mailserver (Postfix + Dovecot) with Roundcube webmail.

Stack

• Docker Mailserver: Full-featured mail server (SMTP/IMAP/POP3)
  • SpamAssassin spam filtering
  • Fail2Ban brute-force protection
  • TLS encryption (modern level)
• Roundcube: Webmail client via HTTPS
• Persistent volumes for mailboxes, state, logs, configuration

Ports

• 25 (SMTP), 465 (SMTPS), 587 (Submission), 993 (IMAPS)

Fixes #8266 /claim #8266