[Dovecot] virtual user problems

[G.Nau]

dovecot 2.0.8 with postfix; transfer postfix -> dovecot by lmtp is fine

Now i have to redirect a couple of virtual email names (like
admin at mydomain.com, postmaster@, webmaster@, info@, sales@ ...) to a
single user postbox named xxx at mydomain.
As I use mysql for the auth-sql, it's returning userhome
/home/<name>/maildir for all sql requests to <name>=admin, postmaster etc.
I also verified that "doveadm user info" is returning the maildir/home:
/home/xxx/maildir
So I assumed, that all mails to admin, postmaster etc. are transfered to
user xxx mailbox.
But it isn't. Dovecot is creating the maildirs /home/admin/maildir,
/home/info/maildir and so on.
What do I miss here to get that virtual users mapped to the correct user
xxx?

Regards
 Birte