Postfix attempts to deliver bounced mail to "bounce" mail account

OS type and version Debian 10.11
Webmin version 1.990
Virtualmin version 6.17-3
Related packages Postfix 3.4.14-0+deb10u1

I’ve freshly installed Virtualmin without modifying any config after going through the setup wizard, then created a mail alias on a virtual server and checked “Yes, send bounce reply”. Accordingly /etc/postfix/virtual contains a line with the alias followed by the word BOUNCE.

When mail is being sent to this alias, the mail is in fact bounced. But the non-delivery report reads:

This is the mail system at host fqdn.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<BOUNCE@fqdn> (expanded from <alias@fqdn>):
    unknown user: "bounce"

This looks like Postfix actually tries to deliver the mail sent to the alias to the local user bounce. /var/log/mail.log says something similar:

Mar  6 08:47:42 hostname postfix/local[16663]: 7D379812CE: to=<BOUNCE@fqdn>, orig_to=<alias@fqdn>, relay=local, delay=0.06, delays=0.04/0.01/0/0.01, dsn=5.1.1, status=bounced (unknown user: "bounce")

In fact, when creating a local user/mail account called bounce, the account receives all the mail sent to the alias, which is configured to bounce all mail.

Is “Yes, send bounce reply” supposed to work this way or is this a misconfiguration?

@Joe do you have any idea, if this is the desired behaviour?

It’s not desired behavior. But, also, it doesn’t make sense to create an alias because you want an address to bounce. Just don’t make that address…if it doesn’t exist, it’ll already bounce.

I have opened a ticket about this, as it seems to be both a useless option (or at least a confusing one), and it also seems to not work with Postfix.

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