NoMailAudit error

[brownh@hartford-hwp.com (Haines Brown)]

I'm trying to get Spamassassin to work with Postfix and Procmail. I
got to the point of creating a "filter" account, and went to it to
test it by running:

  # cat notspam.txt | ./sa-filter.sh -f brownh -- brownh

I message I received as a result lacked body and spam test. There were
at least two reasons:

I installed the deb spamassassin file, and it put things into
different locations than had I compiled it, apparently. The
spamassassin executable is in /usr/bin, not /usr/local/bin. So when I
run this test:

  cat: notspam.txt: no such file or directory
 
I get:

  ./sa-filter.sh: /usr/local/bin/spamassassin: No such file or directory

I simply copied over the spamassasin executable into /usr/local/bin
and now when I run the test command:

  Couldn't open /var/mail/brownh: Permission denied at
  /usr/share/Perl5/Mail/Spamassassin/NoMailAudit.pm line 365

 I get the test message, but it lacks any body and lacks any spam
 test. 

The file NoMailAudit.pm has permission rw-r--r--

Line 365:

    if ($gotlock || $nodotlocking) {
      if (!open (MBOX, ">>$file")) {
        die "Couldn't open $file: $!";
      }

I'm lost. I'm not sure if I can simply copy over the executable as I
did. I'm running this with rmail, not mutt. Isn't mbox for mutt? Rmail
uses RMAIL instead.

Haines Brown