Kentico has page level security you can apply through Roles or Users specifically to make it where a page is not accessable. That's the first option.
If you need to alter the content on this dynamic newsletter page to sometimes be visible, sometimes not, use a Macro in either the Visibility attribute on a webpart/zone to hide or show based on some logic, or use a macro for the Where condition to use 1 query for one type of user, and another for another type of user (say if the user has some attribute that allows them to see the latest news, you can set the where to pull that in, otherwise set a where condition that will only pull in the news that is not the latest).\
See these articles:
Working with web part propterties
Hiding pages based on permissions