Undelivered Mail Returned to Sender

[Mail Delivery System]

This is the mail system at host nnweb.smallboxcms.com.

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

<feedback at thesmallbox.com>: unknown user: "feedback"
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: text/rfc822-headers
Size: 729 bytes
Desc: Undelivered Message Headers
URL: <http://alioth-lists.debian.net/pipermail/debian-science-maintainers/attachments/20220723/fba53c6b/attachment.bin>