make sure to deliver the mail to non-SMTPUTF8 capable remotes unless
there are upper byte values found in headers/envelopes.
this is more-or-less the same as postfix does.

* parse and store original recipients from bounce metadata
* include Original-Recipient fields in DSN delivery-status part
* extend multipart/report formatting for RFC-compliant bounce encapsulation
* improve MIME structure and headers (Auto-Submitted, Content-Type, encoding)