Advanced Mail Options
Give mail control option to clients and admins. Let the choose if they want to enable security except from antivirus and spam filtering. Give more advanced options like mass mail options, the ability to enable a delay before sending an email which is a more secure option and will have more spam-free results. Imagine that someone tries to login to your email server and it sees nothing because you had added a 1 minute delay or so to avoid spammers. Also an option for high security mode which will allow emails only from registered domains of the server to avoid temporary attacks.