>You MUST tell spamassassin what user to run as when you invoke it from your mail processing system. It can't figure this out on it's own.
--> This is a new fact for me which I didn't read at manual.
If then,which process is required?
generally most procmail sorts use spamc -u and pass the recipient name in.. (I'm pretty sure this is $1 to procmail scripts, but I'm no expert here)
