Solved!
Previously I had installed Amavis and co. Afterwards no more and I had restored the EHCP backup with this config included.
I removed in
main.cf:
smtpd_recipient_restrictions =
check_policy_service inet:127.0.0.1:10031 ...
and
smtpd_end_of_data_restrictions =
check_policy_service inet:127.0.0.1:10031Now it works