@mynetworks and spam checks

[Admin Beckspaced]

hello there ;)

i need a bit help understanding things properly. perhaps someone here 
might be able to help?

i'm running an opensuse box with leap 42.1
postfix 2.11.6
amavisd-new 2.8.1

my opensuse box uses things like tripwire and logdigest sending reports 
to my email address
these reports get marked as SPAM occasionally by amavisd-new

i don't want my local emails being scanned by amavis at all and always 
thought that @mynetworks is trusted!

@mynetworks = qw( 127.0.0.0/8 [::1] [FE80::]/10 [FEC0::]/10 10.0.0.0/8 
172.16.0.0/12 192.168.0.0/16 );

meaning ... mails from localhost don't get scanned by amavis. is this 
so? or am i missing something?

as local system emails still being tagged as SPAM i decided for this 
configuration option:

$policy_bank{'MYNETS'} = {   # mail originating from @mynetworks
   originating => 1,  # is true in MYNETS by default, but let's make it 
explicit
   os_fingerprint_method => undef,  # don't query p0f for internal clients
   bypass_spam_checks_maps   => [1],  # don't spam-check
};

i added in the bypass_spam_checks_maps, but still today a system email 
from logdigest got marked as SPAM ;(

what is it that i don't understand properly?

is @mynetworks a special ALWAYS TRUSTED network? how can i whitelist 
emails from localhost so they don't get checked for spam?
or how can i whitelist any dedicated IP address so they don't get 
checked for spam by amavis?

thanks & greetings
becki