Thank you for answer.
We hope to find a easier way to solve this problem.
Something like a config-file but in worst case we will write a custom mail handler.
Following problem:
We need to block all emails from our system to specific email-adresses.
Note, this isn´t done by SPAM-filter blacklist because it´s only for incomming mails.
We need something like this for outgoing mails.
Hope to find someone with an idea for my problem.