Best Practices - Email Servers

Prevent Hackers From Stealing Passwords
Any publicly facing server is vulnerable to attacks from the Internet. These attacks are typically severe against well-known servers like SMTP and HTTP since the TCP/IP port for these services is publicly known. Hackers know that most email servers will contain user login information allowing them to send outbound emails, increasing its vulnerability. This article talks about some best practices to prevent hackers from guess passwords through your email server.

Best practice for specifying a valid HELO and EHLO during email communication
When sending outbound emails, it is important to specify the correct value for your HELO/EHLO commands. Failure to configure these values could result in getting your outbound emails rejected by the receiving SMTP server.