One problem that I'm thinking may occur in future on large installations of ISPConfig is that malicious users may add subdomains to known email-providers. Consider user A knows that people send a lot of emails to hotmail.com . Thus he adds a subdomain to his own site and starts catching emails sent through the system with the catch-all option. Is it possible to prevent ispconfig from adding domains to the postfix local-domains if MX doesnt match? Or Otherwise have a blacklist of domains which arent possible to add into the system. Maybe even wildcard based if you want to block out certain types of keywords in domains.