Here is some information about the Password Recovery feature in WebMail (also known as MailEnable):
1. Password recovery is setup per mailbox and is disabled by default.
2. They get "feature not available" if it is not setup which is what you have been seeing.
3. Each user can click the Checkbox and supply the information to activate it.
4. Here are the details on how to activate the Password Recovery under Options > General > Password Recovery - http://www.mailenable.com/documentation/webmail/Password_recovery.html.