[Koha] Where do "bounced" email messages go?

[Chris Brown]

Gentle Reader

Following on from my previous email about configuring outbound email in
Koha, I have received several helpful replies urging me NOT to "go it
alone" and set up Postfix, SPF, DKIM and DMARC but instead to use an SMTP
mail relay. (I am considering a UK-based service called Arrowmail.)

It looks straightforward to point Koha to a  new SMTP server using the
staff interface, but I have a dumb question. If the recipient replies to
the messages (or the mailer generates an "undeliverable" message) where
does the reply go? How do I set the From: header in the message that is
generated?

Thanks and Best Regards,

Chris Brown