[Exim] Aliases in $domain has to be a local account.

Setting up virtual domains in exim 2.3 (Debian 2.1) seemed nice and easy, but:

after having inserted the recommended

virtual:
driver = aliasfile
domains = dbm;/customer/domains
no_more
file = /etc/mail/$domain
search_type = lsearch

into the /etc/exim.conf I find that the alias entries have to be rooted in an account on my system.

That is: I can't invent names in the aliasfile, eg.
companymail: lars

to have mail to the company sent directly to me. That is, I can't do this without adding `companymail' as a user to the system. What is more:

I can't have mail aliased to an off-site mailaccount, eg.:

postmaster: silly_account@???

I have looked about in the documentation, and from whatI read this shouldn't be a problem, but, alas, it is.

Can someone point me in the right direction?

Lars.