OK, small clarification:
I'd like to disable any mail from 'my.domain' from external networks
and non authenticated users...
...delivered to my users.
Making sure i understand, you are saying you want to stop me from using
my mail server from sending an email to one_of_your_users@your.domain
claiming to be from you@your.domain?
That can be does with SPF records. You publish records that says only
your mail server is authorized to send emails on behalf of @your.domain,
then you use something like "check_policy_service
unix:private/spfpolicy" to deny any email claiming to be from
@your.domain that wasn't sent from your mail server IP.
