I am looking to "exchange" with anyone US based that is running spamfilter in a proper data center.

You will be able to use my spamfilter as a secondary mx and i want to use your spamfilter as my secondary mx.

I currently have 22 domains, however 7 of them are just domain aliases.

On a regular basis the load on my secondary MX server is really low - perhaps 200-300 emails a day, 99.9% of them are spam.

Of course, the real idea here, is that if the main server goes down for whatever reason, the mail will spool to the secondary.

We run on a virtual platform, and in the last 4.5 years we've had little if no downtime on our spamfilter, save for the occasional reboot.

The setup will be such that if an email is identified as spam, it should be immediately rejected. 

Anybody wants to exchange backup MX?