SMTPUTF8 is required, but was not offered by host

We receive many postmaster mails from foreign mailservers with the following message:

"SMTPUTF8 is required, but was not offered by host"

Postfix, Dovecot

Server1: Standard Setup on Debian Stretch
Server2: Standard Setup on Ubuntu 18

When can we expect a fix?
Both systems are clean and no messing around with any config files.
I do not have the time to fill the long bug report.

Thanks in advance!