Simscan on messages from secondary MX

[mogmismo]

We've got two boxes mx1 and mx2.  Simscan and all it's secondary programs (spamassassin, clamav, etc..) work fine for incoming emails directly to the smtp port on mx1, but when mx2 sends a message to mx1, they never get checked for content.  tcp.smtp file is basic, has no reference to mx2, and there are no custom rules in spamassassin for it.

The header of an email (obviously spam) indicates that simscan processed it, but it never gets tagged.

Any pointers as to where I can configure simscan to ensure that it spamchecks from mx2 would be greatly appreciated.

Thanks!