Amavis headers Received: from localhost

[gdavid]

Hi everybody. I'm facing with a small but annoying problem.
All incoming e-mails scanned by our amavis in ISPConfig3 server comes with extra headers similar to:

Received: from localhost (isp.mydomain.it [127.0.0.1])
by isp.mydomain.it (Postfix) with ESMTP id 4D8849EA45C;
Fri, 11 May 2012 15:30:21 +0200 (CEST)
X-Virus-Scanned: Debian amavisd-new at isp.mydomain.it
Received: from isp.mydomain.it ([127.0.0.1])
by localhost (isp.mydomain.it [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id lfYFR3D03r86; Fri, 11 May 2012 15:30:21 +0200 (CEST)

Of course, these are added by amavis when it receive the email to scan and by postfix when the email re-enters after scanning. These actions are performed via localhost (127.0.0.1) ports. Nothing strange.
The problem is that forwarding these e-mail to other mail servers, sometimes are classified as spam because of "localhost" in headers.
I've been googleing a lot to find a solutions, but most of teh strategies sorted no effect.
In details, adding
$allowed_added_header_fields{lc('Received: from localhost')} = 0;
to amavis configuration file (ie in /etc/amavis/conf.d/50-user)
seems to be ignored.
Also, adding
/^Received: from localhost/ IGNORE
to /etc/postfix/headers_check
seems to have any effect.

Can anyone point me in the right direction to avoid that headers?
Many thanks
g