about SPF

[Arvinn Løkkebakken]

I have two questions about the SPF plugin in SA.
What is the difference between FAIL and SOFTFAIL on Helo? When running 
SA with bayes and network FAIL scores close to zero while SOFTFAIL gives 
a solid 3.1. Does FAIL hit a lot of ham? According to my stats, 
SPF_HELO_FAIL gets triggered about as often as SPF_HELO_SOFTFAIL does. 
But I haven't looked to deep after false positives.

Next question. On my qmail-scanner server (in the middle between 
front-end MX and bakend final destination) only the Helo SPF checks gets 
triggered. I have a few thousand hits of SPF_HELO_* every day but zero 
of the other SPF checks.
My front-end MX servers are running Qmail and trusted_network and 
internal_network is set properly. Does it have to do with format of the 
Received headers created by Qmail?

Maybe someone has an URL to some detailed documentation on the SPF 
plugin? That would really do :)

Arvinn