Excuse me if I have not explained myself well...
I have about 100 users registered in my system and they can all open tickets by email normally.
What happens is that I don't want all registered users to be able to send an email and have a ticket automatically opened to them. What I want is to define only that a group of them can do it, and the rest not...
The way I thought I could use it was by banning the emails of the users that I wanted to prevent them from opening tickets by email, but these users stop being able to open tickets from the user portal because they have their email on the prohibited list.