You can auto delete and auto close topics with topic timers.
You could also configure a category to auto close its topics:
I don’t think that’s possible without modifying the code or writing a custom plugin. You could use SSO instead and find a platform that doesn’t do email validation, then set require_activation=true (we don’t recommend you do this unless you have any other way to check your users are valid), check Setup DiscourseConnect - Official Single-Sign-On for Discourse (sso)