[Exim] $domain

Hello,

obviously i still have some problems switching to exim.
Sorry for the last mail where i resent the wrong email.
This is what i wanted to send and which didn't leave the server
for some unknown exim reasons:

i am switching from sendmail to exim now and have a little problem
with the $domain variable. To set the value of file in the
alias director i use this (as proposed in some examples):

file = /usr/local/exim/etc/domain-aliases/$domain

so there is a file called e.g. virtual.dom, but if somebody
sends mail to friend@??? the file host.virtual.dom
is obviously not found.
How can i get the domain without the subdomain ?

Thanks in advance,
Sven