I have 2 mailservers not behind an anti-spam appliance and i have one that is behind a Barracuda anti-spam appliance. Now i want to configure a MX fallback for all the domains. How would i go about doing that? Assume there are a few thousand domains.
I figured placing the domain in /var/qmail/control/morercpthosts will make qmail allow receiving mail for this domain and adding an entry in /var/qmail/control/smtproutes will allow a forward to be setup to the appropriate mailserver... but how do i prevent spammers from using this 2nd MX fallback and spam my users?