Postfix needs smtpd_relay_restrictions under Buster

While trying to send an email on lxdr04.gsi.de (Debian 10.7) I got the following error message:

postfix/smtpd[XXXX]: fatal: in parameter smtpd_relay_restrictions or smtpd_recipient_restrictions, specify at least one working instance of: reject_unauth_destination, defer_unauth_destination, reject, defer, defer_if_permit or check_relay_domains

When I added the default smtpd_relay_restrictions which come with a vanilla Postfix installation the problem disappeared and the mail went through:

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination

I do not know if these parameters are right for our environment. Maybe we do not need SASL authentication.