Excellent & comprehensive security checklist for protection of corporate email resources

http://www.itproportal.com/2014/01/30/email-server-lockdown-a-basic-security-checklist/

QUOTE: Your email server is the collaboration hub for your business, so the availability, integrity, and confidentiality of the information that flows through it is of paramount concern. We’ve got a very basic security checklist here, although you can get more information on groupware security from CERT (Computer Emergency Response Team) and SANS (the SysAdmin, Audit, Network, Security) Institute.

* Use antivirus software * Use anti-spam software * Deploy your groupware server in the DMZ * Limit the size of attachments * Limit the size of user mailboxes * Disable all unnecessary services * Minimize the number of administrators * Disable relaying * Monitor your system * Read security bulletins * Perform regular backups * contact the ISP responsible for repeated attacks * Educate users