How to secure email server?

How to secure Email server?

1.Configure mail relay options carefully to avoid being an Open Relay. …
2.Set up SMTP authentication to control user access. …
3.Limit connections to protect your server against DoS attacks. …
4.Activate Reverse DNS to block bogus senders. …
5.Use DNSBL servers to fight incoming email abuse. …
6.Activate SPF to prevent spoofed sources.
7. Enable SURBL to verify message content
8. Maintain local IP blacklists to block spammers
9. Encrypt POP3 and IMAP authentication for privacy concerns
10. Have at least 2 MX records for failover