Ami go home! 😉🙂

Imaging for a moment all non-company-mail-servers would block all company-mail-servers (like gmail). Would that be a good idea?

I’m against the defederation. The internet and the www are based on the idea of connection.

So just close the ports (or more precise: Do not open them, as “closed” is the default for most software on Linux).

For what you need a firewall on a desktop-client?

What you describe is Zelda 2, but the OP spoke about Zelda 3.