Thanks Bob! Excellent response - so far...
So to get where I want to, one last question (for now):
IF I turn off BSB will I be able to tell WHAT messages BSB WOULD have blocked (had it been on) from the Postini header? i.e. is there a unique code (or codes) for BSB candidates (as opposed to other spam suspects).
What I want to do is get a feeling for the accuracy of the BSB
before I turn it on,
Running for a period with BSB off and identifying messages that would have been intercepted by BSB would do that, plus at any time email went missing I could turn it off and do a test.