I created all@xyz.com alias  for xyz.com domain

Alias : all@xyz.com
To : * 

Note:
I use  *  [ "To create a catch-all use an "*" as alias."  ]  for information Because I want to send mail all users via use all@xyz.com
and  I send mail all@xyz.com adress but I have error below

***************************************************************
This is the mail system at host mail.xyz.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

<all@xyz.com>: user unknown

What is wrong I dont understand Please help me ?