Solaris 10 : unable to masquerade

Hello.

I'm trying to send mail from my newly installed solaris 10 pc but
despite I have read so many web-pages and so many news I'm unable to
have it run due to my incapability to masquerade my hostname.

I use a copy of solaris-antispam.m4 as a base domain file which I
modified to add at the end (after EXPOSED_USER(`root')dnl) the following
lines :

FEATURE(`always_add_domain')dnl
MASQUERADE_AS('not-a-number.org')dnl
MASQUERADE_DOMAIN('not-a-number.org')dnl
FEATURE(`masquerade_entire_domain')dnl
FEATURE(`masquerade_envelope')dnl

I would like to have @kernel.not-a-number.org replaced with
@not-a-number.org

But it doesnt work.

Here is a piece of a returned mail to show that no replacements has been
done.

Content-Type: message/delivery-status
Reporting-MTA: dns; kernel.not-a-number.org
Received-From-MTA: DNS; localhost
Arrival-Date: Wed, 9 Apr 2008 22:07:42 +0200 (CEST)
Final-Recipient: RFC822; foo@free.fr
Action: failed
Status: 5.1.3
Diagnostic-Code: SMTP; 553 sorry, your envelope sender domain must exist
(#5.7.1)
Last-Attempt-Date: Wed, 9 Apr 2008 22:07:42 +0200 (CEST)
--m39K7gIv003474.1207771662/kernel.not-a-number.org
Content-Type: message/rfc822
Return-Path:

Any help would be appreciated.
Thanks