Watermark+Exim don't work together

[Miguelanxo Otero Salgueiro]

Hello List!

    In order to get rid of bounce-back SPAM, I've tried to configure 
MailScanner to use watermarks, but
It just doesn't work. I've just started to do the debugging and asked in 
the freenode #MailScanner channel
and someone suggested I post my findings here, so here I go...

    Setup: MailScanner 4.70.7-1 + Exim 4.50 + ClamAV

    As the first symptom is outbound email having no watermark header, I 
will try to fix that first.
I just greped for "watermark" and found some code in 
lib/MailScanner/Message.pm that deals with watermarking.
Line 340...

      $global::MS->{mta}->AppendHeader($this, $mshmacheader, 
"$expiry\@$hash");

...adds in fact the watermark header to a header set, but as I print 
that set of headers just after
every call to that sub, I can see it gets removed somewhat after the 
antivirus (ClamAV) is called
(I can see the debug messages of ClamAV intermixed).

I tried to find AppendHeader and looks like, as I'm using exim, it 
should be the one defined in
lib/MailScanner/Exim.pm
In that file, line 699 I found this

      $message->{metadata}{headers} = [];

just after something about MIME::Tools and the lack of proper heading 
processing.
I just can say the Watermark header is wiped in that line, and not 
reconstructed after.

Would be glad if someone just takes a pick on this.

Best regards,
    Miguelanxo.