You might also reach out to the postfix mailing lists for help, as you'll likely get better debugging tips for scenarios like this than from a distribution-specific list.
hi jeremy,
thank you for your ideas, i took it to the postfix mailing lists now, but progress there is slow as well. the problem seem to hide very well. link to thread included for future reference [0].
have a nice christmas everyone georg
[0] https://marc.info/?l=postfix-users&m=148248292712509&w=2