Question : How do i configure a MX fallback using Qmail

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?

Answer : How do i configure a MX fallback using Qmail

the answer probably would be adjusting queuelifetime
The "queuelifetime" setting for qmail determines how long messages can stay in the queue. The value is in seconds. By default, your qmail server will keep messages in the queue for 604,800 seconds, or 7 days. However, you can set a custom queuelifetime by creating a file called /var/qmail/control/queuelifetime. The content of that file is a single line containing a number which represents the number of seconds the queue will hold any given message. If you want to set a custom queuelifetime, you might want to whip out the old calculator.