[Exim] Virtual domain router not working?

Hi,

    I have added the following router into my exim.conf file:

# Enable Virtual Hosts support.
virtual_domains:
driver = redirect
allow_defer
allow_fail
data = ${expand:${lookup{$local_part@$domain}dbm*@{/etc/exim/virtualdomains.db}}}
retry_use_local_part


and I have 'db'ed' a file with the following in it:

someone@???:    localuser
another@???:     user@???

But it doesn't seem to work. Any ideas?

Cheers
Scott