critsend (/gridsend?)... what's the(ir) trick?

[Yanek]

Hello list,

A few days ago, I posted this message to the spamassassin user list...
Message follows. Since spamassassin is called by amavis, I've been
advised to start over again on the amavis list.

<original message begins>

Hello list,

Please bear with me if it has been asked already, I searched the
archives a bit and could not find any answer.

One of my email address is subscribed to a site that seems to use
Critsend for its outgoing mails.
Since I like to watch after the SA scores of all incoming mails, I've
noticed that theses mails are _never_ tagged.
I've modified the $sa_tag_level_deflt of amavis to get SA scores below
-100 displayed in headers. I got no score in the headers for these emails.
I then modified the same parameter to get SA scores below -1000
displayed. I still get no score.

Does someone has any idea on how these SMTP providers manage to have
their outgoing mails escape SA scoring?

Thanks 

</original message ends>

I've been asked to post an example of such a message to pastebin.
Here it is:
http://pastebin.com/dpnYY16K

Any clue for me? Feedback will be greatly appreciated :)
Thanks.