Comment # 3 on bug 999902 from Dr. Werner Fink

(In reply to Geert Mys from comment #2)

Where does a mail which report an error do cause an error in postfix?  The
error had happen at the remote server and this remote server returns a *mail*
to the local postfix and the local postfix does deliver this return mail to the
author of the orignal mail ... there is IMHO *NO* error system message
triggered by postfix. Hence there is no error message in the local journal log.

I�m pretty sure that this report is simply INVALID but maybe the postfix
maintainer know more.