No mailbox for root

[Guus]

Newly installed qmail on 2.2 debian/linux works fine, except...

Whenever I send mail to root@localhost I get an error message

<root@mydomain>
Sorry, no mailbox here by that name. (#5.1.1)

A trial installation of qmail does not have this problem.
Similar, almost identical, setup.

How can I create a mailbox for root?

What I want is to forward mail for root to another user.

Tia,
Guus.