The big picture of the plan is:
- debian/ubuntu as os.
- postfix receive and send out to other server.
- spamasasin check inc mails ( and others like amavis,clamd)
- rspamd as milter ( no spamasasin )
- dovecot store , apply filters, fetch pop3/imap
- user preferences for webmail client
- mysql as database for address,domains, aliases
- ssl/tls ( valid green lock )
- 10/10 at www.mail-tester.com
- best resoult for at checktls.com
- hardering
- lock down