At least for #xmpp we have a real time blocklist across the network. and also we have proposals like this aimed at stopping people with new accounts to spam everywhere: https://matthewwild.co.uk/uploads/xeps-tmp/xep-reporting-account-affiliations.html
The proposal above makes it possible to block people based on trust from other servers. For example if the account was created three minutes ago as you said.
But we are missing more help of course :)