[exim] All mail for specific domain to same user

Hi,

I have a running Exim server which is currently only used for outbound
mail. Now I'd like to configure it such that:

All inbound mail for *@*.mydomain.com should be delivered to user X.

For example:

foo@??? goes to /var/mail/X
bar@??? goes to /var/mail/X
bar@??? goes to /var/mail/X

I have the MX record *.mydomain.com in the DNS. As I'd like to support
any subdomain, my guess is that I can accomplish this without setting up
virtual domains. But my terminology is lacking so I don't quite know
what I should look for in the documentation. Any tips?

Thanks.

Morten