[Mailman-Users] Recipient address rejected: User unknown in virtual mailbox table

[franc walter]

Hello,

having a virtual server with ubuntu 8.04 i installed with aptitude mailman
(2.1.9-9u) with postfix, following:

https://help.ubuntu.com/community/Mailman

As admin, i can sign in new mailinglist-users, but if i mail to:

Mailman-request at example.org (where example.org is my domain)

i get a bounce-mail:

Recipient address rejected: User unknown in virtual mailbox table

Same thing if i mail to mailman at example.org.
Sure, i didn't create in my domain in postfix a user "mailman-request" or
"mailman", because i thought this is what my installation and configuration
in postfix checks out.

What is wrong?
Does anybody could give me a hint?

Thank you,

: franc