Whilst trying to use Botnet on my machine running SA 3.2.1 and postfix -
I've come to the conclusion that SA is unable to pickup authentication
headers provided by postfix (smtpd_sasl_authenticated_header yes).

As far as I can see...

From Mail/SpamAssassin/Message/Metadata/Received.pm:
# Postfix 2.3 and later with "smtpd_sasl_authenticated_header yes"
elsif (/\) \(Authenticated sender: \S+\) by \S+ \(Postfix\) with /) {
$auth = 'Postfix';

However, the headers I'm getting from postfix look like:
Received: from MYPC (unknown [77.xxx.xx.xx])
(Authenticated sender: user@example.com)

And the source (postfix/src/smtpd/smtpd.c) seems to back this up:
out_fprintf(out_stream, REC_TYPE_NORM,
"\t(Authenticated sender: %s)", STR(username));

Is this something that needs changed in SA - or something in postfix?