This is a request to implement a feature where you can have specific email account/s used only for communication on active cases and disable the possibility to have new cases raised through that email address and reply with predefined message when such an attempt would take place that in order to raise a tkt user needs to log it via portal. But the same email can be used for replying to active cases already in the system.

For example you have configured specific department with required fields and want to make sure those fields are filled in when the case is created which is impossible to do via creating a tkt via email so you need the user to log the new case via web page.