Alan,

You can add whitelisted IP(s) in SpamFilter so that they bypass all  filtering rules. I'm however not clear on what you mean by "while still performing all the ususal scanning". What kind of scanning do you refer to?

Please note that if your secondary MX is forwarding emails to the SpamFilter server rather than to your SMTP server, then whitelisting the secondary will cause SpamFilter not to filter those emails for spam.
If instead you do have the secondary MX forward to SpamFilter *without* whitelisting it, all of the IP-based filters SpamFilter uses will fail, as SpamFilter will see the IP address of your secondary MX server, *not* the IP of the spammer. Only the content-based filter will work inthis case.

Both of the above scenarios are not ideal. The best option would be to have SpamFilter (or another product...) installed on the secondary MX server as well, as that is the only way to see the sender's IP address and perform IP-based tests along with the content-based ones.

Roberto F.
LogSat Software